Just an uneducated guess. No .jpgs? No .pngs? Sounds like they were working before the experimental Nvidia driver? I'm running KDE. If I go to system settings, file associations, I see every file type my system knows how to deal with. There are about 50 entries in the image category. I'd check that sort of thing first.
i5 3570k, ASRock z77 Extreme 4, 8 Gb Ripjaws 1600, Antec 430w psu, HVR 1600 tv tuner, custom case- marble top, oak face. Carver & DCM Time Window sound system. Mint 14 KDE.