Photography will not reach its bicentenary with anything like the dominance that would have been predicted even a few years ago. Most histories take 1839 as the start date of photography, the year when Daguerre accepted a pension from the French government to make his invention public, and by doing so started the boom that is only now beginning to slow down. For most of that time photography has been unstoppable. It has taken by storm, immediately and permanently, every domain it has touched. Three major industries – making cameras, making film, and processing and developing – depend directly on photography. Many others depend on it for the essence of what they are: fashion, magazine publishing, pop music, advertising, even large chunks of the travel industry… As a technology, it has big powerful descendants, from the cinema to the digital graphics of computer-games or to medical scanners. What I can only call photographic attitudes have spread even farther. It is in photographs that information first became consumable. Immediate, portable, unarguable information is the legacy of photography. Yet by 2039 it is predicted that photography will be unrecognisable, overtaken by younger systems of image-making and itself retrenched into artisan or faddist pockets. At first sight, such a prospect is pretty indifferent: photography was an efficient, sometimes beautiful way of making images. If a more efficient way comes along, then it loses its place and that’s that. But it isn’t so. The technology can move on, as it is already doing at great speed, and no great loss will be felt. Photographers and their clients are already wrestling with digital creation and digital delivery. After a shake-out, they will continue to make their pictures. But the attitudes are more permanent: the photographic way of sharing information is here to stay, even when silver gelatine prints are a quaint old antique, like the tintype or the salt-print.

Photography has been treated through most of its history as marginal. In every generation, photographers have felt obliged to press claims for it (against the prevailing assumptions of its ordinariness) as ‘art’, as objective truth, as a tool of society or science. Individuals have been loud in their admiration for some part of it, but it has always been possible for the majority to ignore them. Yet we have all become literate in photography. So we have become familiar, even dependent users of a technology and the culture that surrounds it, without ever treating it wholly as a culture.

Photographs slide easily from one context to another. They are reproducible and cheap. They are very hard to resist, partly because they are so easy to overlook. Right from the beginning, it has been possible to think of photographs as machine-reproductions and therefore not worthy of serious thought. For snobs, photography was too easy, too demotic, in short: too common to be of any interest. For millions of people it remains just something one can use as a nicely coloured and reasonably accurate form of rapid notebook. Family groups at weddings or Christmas, a few rolls of film every holiday, and never a thought given to how it is used or what it can mean. The relatively high visibility of certain kinds of photographic activity have made it possible to think that it has finally ceased to be regarded as marginal. A fuss every so often (about a Joel Peter Witkin, or an Andres Serrano or an ad campaign that gets itself noticed, even the occasional news photograph), and it is possible to think that photography itself is on the cultural agenda. To some extent, it has become so. But the reality is still marginal. Most of us never stop to think how a photograph works or what it does. It operates beneath the skin.

It should be obvious by now that it is not marginal at all. If we live in an age of communication, and we do, that is palpably due to photography. We all use it, daily. We are influenced by it, informed by it, all the time. Selling things has been one of photography’s prime roles for generations, and nothing yet fills that role so well. What we know about the world is very largely due to photographs, even what we know about ourselves. The purely practical applications of photography are global, numerous, all-encompassing. From medicine to state control of citizens, from research science to high-art, from family memories to instruments of change, this has been not a marginal activity at all. Photography really did explode: like the big bang, its expansion has slowed down and its effects are cooler, but it’s still expanding. Photographs are everywhere, yet how they have worked and what they have done is still more or less secret. We are supposed to believe they just are. Until very recently, for example, no British newspaper has had a full-time photographic critic. This is extraordinary: all serious newspapers feel obliged to have writers on opera, on rock-music, on architecture… Part of the reason is in photography’s very success: as artefacts, photographs are so common that there can hardly be the tight relationship between distributors and the press which exists in other domains. People do write photographic press-releases, of course, and newspapers duly re-heat them. But they cover an insignificant part of the volume and variety of photographic activity. For opera, that is not so. Therefore opera seems, when viewed through the press, to have a unified culture which photography is denied. That doesn’t make photography marginal.

It is clear that the entire history of twentieth-century art has been centred on photography. Artists have either fled from it to produce things they felt the camera couldn’t do, like abstraction, or have rushed to it to make its strengths their own. Pop Art is unthinkable without photography, and so for different reasons, is Degas. Many, many artists use photography directly as a technique: David Hockney, of course, became something that might properly be called a photographer; he made works whose finished surface is on light-sensitive paper. He has often written brilliantly on photography. (His most recent book, Secret Knowledge, is a remarkable attempt to push the start-date of photography back by several hundred years). Francis Bacon, in contrast, never wrote more than en passant about photographs, but still he was by culture a photographer. Not that he used a camera to make his finished works. But his choice of what to exclude and how to frame, always the primary photographic mode of selection, looks very photographic. Those blue ovals in the faces of his portrait-sitters look like parodies of the flares from a lens. He often worked from photographs. Everything he did, in fact, was understandable mainly in terms of an audience more literate in photography than they were in paint. There is hardly an artist to whom an extended definition like that would not apply. To ignore photography is always to risk missing the point. I remember that the Royal Academy had its first-ever photographic exhibition in 1989, to celebrate 150 years since Daguerre. The Academy, forgetting that it was almost the last institution to do so, allowed itself genteelly to boast at how daring it was to turn its attention to photography. It looked ridiculous. Almost every artist the Academy had shown for years before had been centrally preoccupied with photography, for or against, overtly or discreetly. The Academy wanted to break box-office records, of course, and I dare say duly did. Photographic shows do that, and every curator who wants to get his turnstiles clicking knows it. Nothing wrong with that, but photography isn’t exceptional in the art world, nor is it snobbable. It certainly isn’t marginal.

The effects of photography are pretty clear in the field of fine art, where the work that photography has done is visible and traceable and, in the end, nobody much denies how important it has been. In other fields that is not so. In medicine, for example, photography and its derivatives are useful tools whose use is now taken for granted. The picture, the scan, the x-ray are everywhere. Is it absurd to think that doctors now think photographically? The rest of us do. The vast central presence of photography is visible well outside the art-world.

I suppose the central thing in photography has been its relation to the fact that it depicts. Photography has always had a particularly intimate relation with the real world. We believe photographs because we identify in them objects that have been unchanged by the process of being included. It’s false, of course, and always has been. One of the first photographs ever published depicted an apparently headless horse on a Paris boulevard. The horse had stood still through a long exposure, but had moved its head enough to leave no trace on the plate. We can all see that photographs can present illusions or interpretations, and indeed we all do it all the time. Yet we remain un-cynical about photographs. We do not necessarily expect photographs to be “true”, but we at the very least have a very strong disposition against suspicion of them. The immediate reaction is to believe what they depict to be the fact itself. The reason for that is precisely that we have been used to treating them as marginal. By treating them for decades as non-serious carriers of messages, we have allowed photographs to get behind our defences against false messages or skewed messages in a way that is unthinkable for any other means of communication.

Or, at least, that used to be unthinkable. Because photography has been so successful that it has effectively exported the ways of thinking that have developed through it. We glance at a photograph as a complete frame of information. A photograph is beyond question, beneath question. It just is so. Under a wholly mistaken double assumption, we understand photographs to be factual, and marginal. We treat photographs as if they were beyond analysis. It has become habitual. So when it is so often written that we live in the information age or the age of communication, it is quite true. Vast information, nearly instantly accessible. But the analysis to go with it lags far behind. We have learnt from photography to absorb quickly, efficiently, fairly uncritically. Our view of the world really is made of images now. To see a war or a pop star is not the same as to understand causes or to make a critical judgement. It is always easier to move on to the next image than to stop and make an effort to digest the last. From photography, we grew used to experience without analysis. And that has now spread far beyond.

I do not mean to imply that no thought is ever given to photographs and how they work. It is, and is often important or interesting. But it is exceptionally rare in proportion to the vast scope of photographic activity. The language we use about photographs is so sloppy as to lose all meaning. In advertising agencies the people who deal with photographs are quite normally shockingly illiterate in the art-form from which they make their money. So a photographer who wishes to use the ordinary cultural resources of any other medium – allusion, say, or parody or quotation – is prevented from doing so in any but the crudest way. The fashion business, which, after all, depends almost entirely on photography for its visibility and therefore for its presence in the market, is even worse. The most analytical comment the fashion business will tolerate on a photograph is a hyperbolic “Great image!” without any possibility of analysis at all. Even where there is sensitivity to pictures, as on occasional newspaper picture-desks, the tendency is to understand them without being interested in articulating the thought. To analyse a photograph is thought for the most part to be an academic luxury, or perhaps a pretension. Yet photography is a perfectly ordinary cultural activity. A photograph is good or bad for analysable reasons. As the volume of available photography increases hugely (because pictures are perhaps the easiest thing to find on the internet now), the temptation is always to plump for the one that ‘does the job’ without looking for the one that does more. And the users and the viewers and eventually the creators of the pictures expect correspondingly less from each one.

So this fantastically successful medium has exploded into the world, without generating any cultural antibodies that might have defended us against some of what it can do. The effects have been far, far wider than simply in the reception of photographs.

Photography has profoundly changed the big things. Aesthetics, for a start. Ugliness and squalor slide onto light-sensitive paper as easily as grace and elegance. A good photograph may well be (often is) of revolting things. Well-depicted has replaced worth depicting, and that simple shift has spread far beyond the photograph itself. The message is clear? It’s a good photograph. Which is a seductive compression of communication that has had tremendous success when exported. I detect photographic roots in the culture of the sound-bite, where the unquestioning absorption that we learnt from photography has been passed on to other ways of receiving information. Are the shortening attention-spans of today attributable to photography? Perhaps in part. I see a kind of aural photography in popular music, where increasingly the things that go with the music (clothes, attitude, the video, the context in which it is offered) are more important than the music itself. The music becomes just a shorthand for all those other things, neatly packaged into itself.

At one level, the preponderance of photography as the means of distributing quick information has meant that considerable effort has gone into making things look good in photographs. Facades of buildings, kitchen gadgets, authors, politicians all have been submitted to the process of creating for them an “image”. If merely for good presentation, no harm done. But those things which cannot be shown in the picture will eventually no longer be built into the thing itself. When the building no longer works well as a succession of spaces for circulation and for shelter, but only in the photograph, then surely something very important has been changed. There is a word which explains this process. Photogenic is an abominable word which means that certain things have a tendency to look good in photographs. In fact, there should be no such thing. A great photographer will make anything look right in his picture, not because it was so, but because he had something to say about it which allowed him to make it so. But unfortunately, we now believe in the photogenic. More and more we expect things (and people) to look just so. Then we assume, quite wrongly, that they have whatever it takes to be so.

When the short-hand no longer stands for the complex of functions or the complex of messages about them but becomes all that we need to hear about those things, then the wealth of possible meaning has taken a very sharp dip. Photography is often used illustratively. What it then does depends on elements that are not in it: context, caption, accompanying text, page layout. That is going to become more so. The shorthand no longer referring to very much beyond itself, it will be necessary to go back to the fuller explanations. Contemporary art photography has been dependent on words for a very long time. You see a boring view, not apparently composed at all, of a German city, unpeopled? You are supposed to see a critical reflection, no doubt richly informed by the work of the Dusseldorf School, where our subject-status as citizens is called into question by a scrupulous objectivity of vision. It’s still a boring city-scape, but it’s supposed to have a cultural context. Any photograph can be made to stand as the shorthand for something if only the right jargon can be found to go with it. The whole world has been photographed. For a picture to have value now it needs to fit into a pattern of thought which is not photographic. No longer a very effective shorthand, more of a footnote. Photographic criticism almost never asks whether the thing is beautiful. Fogeyish. Old-fashioned. Is a Martin Parr picture beautiful? A Don McCullin? Beautifully observed, beautifully marketed, beautifully slotted into a context. We understand those and can talk about them. But beauty? We don’t talk about beauty now. We’ve found a word to allow us to duck that. We’ve found a weasel-word. We talk about design. As photographs become increasingly denuded of meaning in themselves, they increasingly become raw material for others to do things with.

A picture-editor on a magazine, a graphic designer, a curator, a propagandist, an art-director does not have to be literate in photography to use pictures. Some are. Many more can’t be bothered. They assume pictures to be transparent and beneath analysis. Use them like that, and surprise! they’re becoming like that.

Photographs won’t be the thing in the next decade. There are too many of them, doing too little work. My guess is that words will make a strong comeback over the next few years. To the readers of this magazine, that sounds absurd. Surely words have never gone away? But for years they have. A whole generation doesn’t read magazines, so much as absorb them. In the culture of the video-game and the internet, images have been the grabbing thing. But they don’t grab enough anymore. Not because they cannot, but because as audiences we have been trained to assume them to do no more than that. As consumers, we’re beginning to resist images. We’re savvy now, we think, we’re fly to the kinds of reactions distributors of images want us to have. We’re immune, we think. But we’re not.

Photography used to be like tape-recording: a system that had some possibility of selection and of editing (and some inescapable distortion) but that maintained an essentially linear relation to fact. As such it was so useful that it boomed and boomed and blew into every corner of our lives. Don’t believe it? You’ve probably seen more than a hundred photographs today, without trying. On the bus, from the bus, in the paper this morning, in posters, on stamps… All absorbed, all filed in the mind without explanation or crossreference. Precisely that absorption under the bombardment has become the standard way of receiving information. Even when that information is no longer photographic. A headline scanned, a sound-bite half-heard, a brand name imperceptibly become familiar, an argument sketchily reproduced from a handful of buzz-words. That is photography’s legacy to the information age. Meanwhile, photography itself, as a set of technical procedures or as a connected cultural activity, means less and less. We proved that we could make photography touch everything, mean anything. That was the big bang. Nothing has been left untouched by photography. But there’s nothing left in the middle, where the explosion occurred. Or rather, there is. There’s debris. And the debris which is going to be flung farthest, and which will appear in the unlikeliest places, is that to be aware of something is somehow to be informed about it. That’s the real legacy of photography. Before photographs, it was usual to experience and then to analyse. After them, we can expect to experience many times more (even at the very slight level of a second-hand reference) and analyse less. It is already happening, all over the place, and we hardly noticed. Photographs themselves often fade; as photography ceases to be an avant-garde activity we can see that the marks left on our culture by photography itself are indelible.