That is a good idea and I might also add that I would have it in a frame at all events that I attended. The shame might stop them, but it might make them mad and you might lose all your caches.
(1). Make yourself a flyer including the pic. Go to a copy place(kinko's cost .10 a copy) and make yourself about $3.00 worth of them. Then post them around your area near caches(your's and other caCHERS TOO) for other cachers to see. Also post them in high profile locations around town.
"Have you seen this person? He/she has been stealing other people's stuff!"
(2). List a new cache with the picture " No Honor Among Thieves" That way ALL geocachers in the area, not just the ones on here, will know what kind of person he is or isn't.
Another idea would be to confront them with evidence and ask them to stop or I would spread it all around the Caching community.
The other ideas that I have would not be very nice and might include booby traps, explosive devices, inkpacks and/or a shotgun with remote control via webcam????
I hate a thief more than a crappy log writer.
I have friends in overalls whose friendship I would not swap for the favor of the kings of the world.
Thomas A. Edison