I have covered this a number of times. Here are a few:

https://www.reddit.com/r/AskHistorians/comments/8hkvlj/nsfw_in_bram_stokers_dracula_1992_when_dracula/

https://www.reddit.com/r/AskHistorians/comments/1v38ja/what_are_the_earliest_known_pornographic_texts/

I also discuss this at greater length in my book. But the quick and fast answer is that the concept of pornography as we have it originates from about 1850 or so.