@ben the most reliable way to check is to open up the game. legit retail games have mask roms with (usually) proper markings on the chips. as of know making a reproduction cart requires an eprom (the kind with the window on top) or an eeprom (I don't know what those look like by they would be different than a mask rom). there are some odd items like test carts that were built with eproms, or very rarely you find a real game that has eproms from a repair or some other procedure, but these are edge cases.

if you only have pics to go on, doing comparisons with images of know good examples will cover a lot of issues. for example, the label on OP cart is dimensioned wrongly. you can compare with scans to see that the image is zoomed in, as there isn't the proper space around items at the edge of the picture. the back label is also wrong for this cart, but that's less reliable since a lot of the F2 carts coming out of central/south america are likely to have the back swapped with whatever is available in order to get rid of the extra label slapped on the back.