I was just watching a uk tv show about how some artists years ago used to insert anamorphic objects into art.
I have posted two samples but others are done so you have to look at the art at a certain angel to see the image.
I was thinking this could be used for porn.
In one extream way, one could think that the films and photograpgs are given away free, but to see them you have to buy the 'tube' to watch (ie place it on your pc screen).