I'm not sure if yours is the same problem I had, but I fixed a QuickTime slideshow image problem in Safari by deleting the browser cache, deleting the related plist files (they recreate themselves automatically, although you might have to enter the serial number again if you have the pro version), and restarting Safari. Hope that helps.
com.apple.QuickTime.plist
com.apple.quicktime.plugin.preferences.plist
com.apple.quicktimeplayer.plist