Its against TOS so any difference or thing should be there between images and ads and users must never be shown that the links are leading to image details.
You are running in to problem.. Google TOS has a clause in it it against misleading the google adsense advertisements with images and headlines above or below ads.. Sites which make good adsense revenue may be let off but sites with small clicks may be punished..
Why take risk when you have many established techniques.. I would suggest you to put a divider between two..