Luckily for my wise and erudite audience, Mike C. has written an actually interesting piece, which if you have not yet read (and why not? Hmm?) you ought to read. It's the sort of thing I aspire to write when I am not consumed with fits of bile, and he makes a most excellent case for collage and related forms that begin with photographs and end up somewhere else.
Since this is very much a Thing (especially if we add in, which Mike doesn't, your basic "heavily photoshopped thing that look like a photograph but isn't any more") it's worth a good think and a spirited defense.