Photo wrong thumbnail
A couple of things you can try:


Open the folder in Finder - click on the Actions button- select Show View Options - put a check next to Show icon preview. If it's checked, uncheck it, close the window, open it back up and check it again
Head for your home folder - Library / Preferences - move the com.apple.finder.plist file to the desktop - log out and back in. If this fixes it, you can delete the file. This is going to reset all your Finder preferences to default.
the thumbnails are stored in a folder called com.apple.QuickLook.thumbnailcache in a subfolder of /var/folders. The quickest way to locate it should be to run sudo find . -name com.apple.Q*. You could move that folder to a different location and restart the Finder process (killall Finder) to force a recreation of the thumbnails.