I was just thumbing through "marvels" and it does look like they're photographs he's using. For one thing some of the poses shown would be impossible to hold for too long, like that captain america one,
Second, if he's painting these people as models wouldn't all the pictures be in the same place like his studio.
Some of this dude's ripoffs are more inspired by then completely ripping off, like that cover from Sojourn. He used the position and the boobs, but the rest of that cover isn't stolen.
I still have alot of respect for Ross and Land, and I still believe what they do counts as art and not tracing.
*later that day
I checked out that link rachael posted, it is very interesting and kinda funny.