I've got to try this out soon - if it works it could really be brilliant. The idea is that you take a number of pictures (3+) of something touristy (i.e. something that people and cars are going past and getting "in the way"). Don't have to be perfectly the same, just close.
Then the program looks at all of the pictures and removes anything that isn't in all the pictures (i.e. people move, cars are gone, etc).
What you are left with is just the main object/building/thing without all the "noise".
Wonder how they do it?
Cool Tool: Tourist Remover