I agree with Phantom. If you don't want the images to matter, then specify "NO IMAGES." Because as he said, if we all just used a stock photo (like a picture of a dagger for a weapons competition), then the boomerang idea would never have come up since a boomerang isn't a dagger.
Even stock photos would severely limit the competition.
I like the idea of competitions where you HAVE to use a certain image, but it creates an entirely different creation environment. It's like the difference between an unupped tourny and a special rules tourny: both are tournaments, but you need different mind sets to make decks for them. So the card idea competitions shouldn't solely be done this way.