Do the image files become corrupted, or is it only the display of the images? Are the images o.k. after rebooting? Do you have a current backup, just in case something is seriously wrong?
I'd try to reset the NVRAM:the display resolution may not be stored correctly, see When to reset NVRAM or PRAM
Also I'd make a hardware test, to check the RAM; you might see similar artefacts, if the RAM has a problem, see:
Besides checking the hardware, walk through the usual trouble shootings steps:
Post back, if this does not help.
Try the above first to make sure it's not a hardware issue
After that, if you still have issues, fix the permissions for your home directory, and then run repair disk permissions (from the Disk Utility).