Stuff stays on the internet for a very very long time.
On the other hand, there's so much porn out there, it'd be like finding a needle in a haystack the size of the internet.
Thing is, as long as the pic/video is not terribly unusual (like a fist in the ass) and it's not tagged with text around it that can be searched, then the chance of finding it is basically nil.
Think about how many blow job pics there are out there. What's the chance of someone seeing yet another blow job pic of 300 million bj pics and identifying the person? Unless that pic was posted in a forum or a gallery somewhere with the words "JESSICAXXX" around it?