I'm the one who has been uploading the sadly somewhat grungy Intellivision covers.
Most, if not all, of the Intellivision boxes currently in the database are recreations from thecoverproject.net (the one you're asking about came from http://www.thecoverproject.net/view.php?game_id=5825). The x-by-2100 resolution is the giveaway, although if you look closely at the small fonts, you can tell they're not quite right. The backs of the boxes are much more obvious.
I wish I could find better scans of some of these boxes, but Intellivision was a lot less prevalent than the 2600 back in the day, so there are far fewer sources available, especially for the backs.
I've also been replacing a few Atari 2600 thecoverproject.net recreations here and there. These also look very nice, but they're a little too perfect, and the kerning of the fonts is usually a little off.
Anyway, thanks for asking about those boxes rather than just rejecting them out-of-hand.