beanieb, I think you misunderstand the concept that the Victorians 'invented' pornography. It's not claimed that the depiction of sexual acts did not exist before the 19th century, but that the victorians were responsible for naming it. So they invented the concept of "sexual imagery which is intended only to sexually arouse", and they gave such material the name "pornography" which means literally 'writing about prostitutes', or (interestingly) in some etymologies 'writing about female slaves sold for prostitution'.
This was associated with the Victorian obsession with classification and taxonomy, and can be seen as an attempt to control who had access to such material, at a time when photography and photographic reproduction was becoming democratized as a technology. The governing class feared that the dissemination of pornography would be expanded by photographic reproduction (as it has been by every new technology, as you say) and would 'corrupt' (ie distract and destabilize) the working-classes whom it needed to build the Empire etc.
They passed the Obscene Publications Act which made it illegal, and the word appeared in the dictionary for the first time in the same year.
These events were also associated with the discovery of Pompeii, with its vast wealth of erotic imagery on public display, and the immediate burying of this material in the Secret Museum at Naples. Like the Secretum at the British Museum, this was accessible by 'gentlemen and scholars' only.
The difference, incidentally, between the attitudes to sexual imagery of the Romans and the Victorians encapsulates the meaning of pornography. A fashionable Roman displayed sexual imagery quite openly in their homes - above the dining table, say. They hadn't developed an idea of privacy (which obsessed the Victorians) and consequently were as happy to have images of sex as images of hunting.
Sorry, this is a rather dry precis. It's actually quite an interesting area - there is a documentary series called "Pornography: The Secret History of Civilization", the first episode of which deals with this period.
So I'd completely agree with Dittany that pornography as we know it is imagery of sexual acts, reproduced (crucially) on an industrial scale; and that therefore most men of the 19th century wouldn\t have had access to it.
I don't think I'd place the beginning of the 'mainstreaming' of porn post-fifties, as Dittany does, though - I think that the invention of film (another case of technology expanding porn's reach) was key; as was the beginning of democratization of travel, to Europe and the Colonies, which exposed the middle-classes to cultures which didn't legally restrict access to sexual imagery. I'd say 1920s/thirties.
But the real turning point came later, in the 70s, when porn, by an astonishing sleight of hand, managed to associate itself with progressive politics, and porn films started to be shown in mainstream cinemas in the States.
And then again in the early 90s, fuelled by the availability of VCRs, which meant that porn could be viewed in the privacy of your own home. This caused a massive expansion in the industry (as well as the depressing development of 'gonzo' porn) - a huge section of LA became Porn Hollywood.
Once porn has become truly industrialized, it is bound by the rules of capitalism and must continually find new ways of making its consumers buy what is effectively the same product. It has done this by becoming simultaneously more 'extreme' and more 'mainstream' - a product, nothing more, nothing less.
It has been an incredibly successful marketing coup, this repositioning of porn as a consumer choice like any other.
Anyone who dislikes porn is now defined as 'anti-progressive', since modernity has been carefully associated with consumption, and freedom has been redefined as 'freedom to consume' and/or 'sexual freedom' (as opposed to, say, political freedom, which would be very dangerous).