Optical delusions are when your eye sees one thing in an image because it's become accustomed to that kind of image in that context. In the cases of the following images, if you see the "dirty images" then you, unfortunately, have a dirty mind. If you see what's really there, then you're a healthy, good-hearted, well-meaning, functioning member of society.
So here's a list of things that look dirty, but aren't. All of these pictures (and one video) seem dirty at first, but when you look closer it turns out that not only would those be horrible pictures in these contexts sometimes, but that you've brought dirtiness into the pictures yourself.