Just managed to dig out some information about something I've suspected for a while - that the emergence of modern art is indeed roughly synchronous with the invention of photography. Using a post hoc ergo factor hoc type of argument, I'm therefore convinced that there is a clear nexus here. That faced with a superiour way of representing reality, artists turned to alternative inspirations and muses for expression of their talent. If you wanted a true-to-life image of yourself or your street corner, you would call a photographer, not an artist any more. What was a poor artist to do? Enter Impressionism, Surrealism etc. Check out these links...

http://www.rleggat.com/photohistory/
http://www.artelino.com/articles/modern_art_periods.asp

notice the dates.