Yosemite: Corrupt quick look images Ever since my transition to 10.10.5 Yosemite, quick look keeps corrupting the preview images every now and then. Sometimes is persists until reboot, other times it goes away after a while. The image files themselves are fine and open and display in any application. 

Any ideas? 

Example:
This may help : http://encase-forensic-blog.guidancesoftware.com/2014/05/examination-of-mac-os-x-quick-look.html or https://discussions.apple.com/thread/1289781?tstart=0

You should be able to rebuild the so called ThumbnailCache on your mac.
This should work. hope this helps :)