Stop making this into what it's not.
EmeraldTiger, it's just a placeholder.
I sense miscommunication.
"False card" is too vague of a term; something along the lines of "the copies do zero damage and have non-functioning abilities, but to the opponent, they appear to be regular cards" would be clearer. The Notes section is for clearing up any and all ambiguities/interactions that may arise, and being in-depth about it.
As for the art being a placeholder, it's perfectly fine to just leave the picture blank. Sure, it won't be accepted for Crucible submissions, but neither will a card with art of questionable origin.