Before you read what I copy pasta below remember that I have no real say in the value of the cards, just providing information.
"There are many alterations consisting of extending the card’s original art towards the edges; in those cards, the name, mana cost, original art, card type, and rules text are easily recognizable. For this type of alteration to be legal, the card must retain its original borders, either black or white. We wouldn't allow this example in tournaments since the alteration has covered the card’s original black border. If the card would have kept its original black border, it would be tournament legal."