Very difficult but a really nice puzzle.
I looked at this for quite a while last year but got nowhere. Yesterday however I watched the Champions League Final with Richiecactus and he happened to mention something. That reminds me of a Woking Wonders puzzle cache I was looking at last year I said. Within a few minutes I'd found the puzzle in question. The images were then quickly discovered, and so then I knew the identity of the odd one out.
I went looking for it this morning with The Bobcat. Unfortunately I'd mistyped one number in Google maps and the co-ordinates ended up in Private land. We circled around it: a cuckoo seemed to be taunting us right at those coords but we knew it couldn't be right.
So we went back home, discovered the error and returned in the afternoon. My cachers eye suggested a likely hiding place but the GPS said we were still 150ft away I didn't trust it and within a minute The Bobcat had the cache in his hands. I watched the GPS as it only now sheepishly agreed with us: the numbers gradually going down all the way from 150ft to 4ft.
Incidentally it seems that a couple of cachers found this by accident(!!!) about three weeks ago - but presumably didn't log it here as they didn't know which puzzle it was.