I have answered this a few [times](https://www.reddit.com/r/AskHistorians/comments/1v38ja/what_are_the_earliest_known_pornographic_texts/] before and you might be interested in my book but here was the most recent summary of this:

I'm adapting this from some older answers.

Here's the tricky thing about your question--do you mean 'porn' in the sense of moving visual art of people doing erotic things? Then in 1894 Edison's studio recorded a vaguely erotic short, titled Carmencita, which featured a Spanish dancer who twirled and posed on film for the first time. The short was considered scandalous in some places because Carmencita's underwear and legs could be seen in the film. A couple of years later, in 1896, the same studio recorded The May Irwin Kiss, an 18 second film of a Victorian couple kissing (in an incredibly awkward and forced manner). According to Maximillien De Lafayette, this scene in particular caused uproar among newspaper editorials, cries for censorship from the Roman Catholic Church, and calls for prosecution—although these calls do not seem like they were followed up on.

Or perhaps you mean film of people actually doing the deed? Then the oldest surviving work we have is L'Ecu d'Or ou la Bonne Auberge, which was first distributed in 1908--and features a man coming to an inn somewhere in france. The inn has no food, but the inkeeper is desperate for food and offers a very different type of food -- his daughter. And then, just because a third woman has to come and join in on the fun. However, this film only survives in a few places now, censors managed to destroy most copies of this film.

The earliest surviving American film, available on Wikipedia of all places, [THIS LINK IS LITERAL PORN, YOUVE BEEN WARNED] is called A Free Ride, and dates from 1915. These types of works were typically shown in brothels, until film projection equipment became cheap in the 1930s.

As with photography before it, and books before that, film eventually became cheaper and more widespread, began appearing in the alleyways and under the counter at stores, and eventually lead to arrests, prosecution and jail time. The Czech movie Ecstasy (1933), for example, featured scenes of nudity, and perhaps the first female orgasm shown in a major theatrical release. The scandal of these scenes lead to cries for the seizing and banning of the offensive material, and lead to the Hayes Code in the United States, which successfully banned erotic material from Hollywood movies for the next 30 years. Full freedom of pornographic expression was not available until 1988's California v. Freeman, which effectively legalized hardcore pornography.

Or do you perhaps mean "porn" as in the concept of pornography as a whole? 'Porn' as we know it is a relatively recent thing, dating from the early 1800's or so, 1857 is when it was really written into law in our modern understanding of it (in england and France, a few years earlier in America). So 'porn' as we know it is only about 150 years old!

This is really surprising to most people, as they tend to think, as you do, of the Karma Sutra and other things as pornography. But they're not, or at least in their original contexts they were not

“the explicit description or exhibition of sexual subjects or activity in literature, painting, films, etc., in a manner intended to stimulate erotic rather than aesthetic feelings” (OED)

Although pornography is a Greek word literally meaning “writers about prostitutes,” it is only found once in surviving Ancient Greek writing, where Arthenaeus comments on an artist that painted portraits of whores or courtesans. The word seemed to fall more or less out of use for fifteen hundred years until the first modern usage of the word (1857) to describe erotic wall paintings uncovered at Pompeii.

Several ‘secret museums’ were founded to house the discoveries. However, these museums (the first of which was the Borbonico museum in Naples) were only accessible to highly educated upper-class men, who could understand Latin and Greek and pay the admission price.

As literacy rose and the book market developed in England and it began to seem possible that anything might be shown to anyone without control, then the ‘shadowy zone’ of pornography was ‘invented,’ regulating the “consumption of the obscene, so as to exclude the lower classes and women.” (Walter Kendrick, p. 57, The Secret Museum) Critics and moralists responded to the growing market, rising literacy, and the developing public sphere by expressing a deep anxiety over the impact and influences of erotic works. Erotic discourse began to be inextricably linked to a ’type’ of work that supposedly had undesirous effects upon the English public. In Lynn Hunt’s words then, “pornography as a regulatory category was invented in response to the perceived menace of the democraticization of culture.”