This image clearly shows the difference between the Authentic (right) and the Counterfeit (left) pins. Source.

This is most famous of bootlegs: the original Donald Duck "Wet Paint" Mystery Release pin.  Although you can still see these pins on eBay on occasion, for several months they were being sold for hundreds of dollars until someone smartly listed both the real and the fake pin side-by-side on Pinpics.

Here is that picture...there's not much difference exept for color between the valuable real pin (at right) and the counterfeit (at left).