[seanofjapan]

That raises an interesting question though: how much do you need of a card for it to still be considered a card?

51% or more? I think that is the standard for dollar bills, but it seems a bit low for a baseball card.

Anyway, establishing that standard would tell you if you can say you have a 1952 Topps Mantle, or if you have a piece of scrap cardboard.