Beyond “Your Opinion” the alter has to meet the MTR requirements. Which means some heavy alters, for example that paint all the borders, will not be a judgment call. They are not permitted unless you have a means to *know* the card is the actual card and a real card.
Andy hit the nail on the head. This is the process I follow when examining alters:
Step 1: Does this alter meet the MTR requirements? (name, cmc, strategic info, offensive, preserve artwork)
STOP IF IT DOESN'T
Step 2: Can an average player be expected to recognize this when seeing this card? (Think resolving
MemoricideSTOP IF IT DOESN'T
Step 3: If this is a judgement call, make sure you consider the ramifications of future events where this player will seek to play this card.
Step 4: Explain to the player “I'm going to allow this at this event; be sure you always check with the Head Judge before you play in other events.”
Edited to reflect Scott's Step 4
Edited Jeff S Higgins (Feb. 4, 2015 03:29:16 PM)