"Backups" are illegal in some countries and not in others... in USA Roms are totally legal as long as you own the original copy of the game, same with ISO files. As long as the rom/iso themselves is not redistributed in the US your fine. Rediributing roms/isos in Canada and UK are totally legal, to DOWNLOAD them you must already own the cart or disc.
Ripping textures from the rom dumps, OR from screenshots is technicly illegal, but its being transfered back over to a nintendo product and not another product for sale or for advertisement for yourself, its technicly advertisement for nintendo, so they will not bust you even though its technicly against their terms. I would recommend a disclaimer stating "all textures and art belong to their respected owners" and a "special thanks to nintendo", wouldnt hurt.
Now, back to the OOT Cel-mod.... Please.