The Webmaster's Revenge
Suppose you take a lovely picture of a wedding, and decide to use it on a website promoting your wedding photography business. Like this: Suppose you then discover that this picture is being used by other sites who can't be bothered to take their own. And, what's more, they're even linking to the image directly off your server so you're paying for them to be able to display the image. What do you do? You change the image that their sites point to to a picture of the ugliest dog in the world: So their sites end up looking like this: And this: Beautiful.