I'm 99% sure all 3 carts in the first picture are fake, as is the B&W case Batman Returns (the top cart).
The labels on each of them is pretty much a giveaway, except for the Shadow Dancer one I guess.
I grew up with a Japanese Mega Drive, and most Japanese MD carts have a different shape to that of the Genesis ones. They have rounded sides with horizontal ridges all the way down them, unlike those in the picture which have the smooth "shark's fin"-type of side (can't think of any other way to describe them, sorry.)
Also, I vaguely recall original carts
usually had a brown/bronze chip/wafer inside the cart, unlike fakes which usually had white/silver ones.
Um.. I haven't touched my MD in years but that's as far as I can recall. Pretty sure these are good ways to spot for fakes, though not entirely foolproof of course.
Hope that helped.. else I'm sure someone who knows better will come along and correct me soon enough.
