Visible crew/equipment: When Crown nearly walks into the lorry at the beginning you can see cables of sort in the left hand mirror from the shot inside the lorry. (00:02:50)
Visible crew/equipment: When Thomas Crown exits the museum after having stolen the Monet, we see a couple of strange characters, probably crew members, standing on the ledge of the building just behind the cab he gets into. The man with the mask is the most interesting. (00:20:15)
Answer: I believe that the Monet that Crown hides in his study is not the one that was stolen, it is a copy that he already had prepared. He can enjoy the copy knowing that the original (with the broken spreader bars) is also in his possession. The stolen original then goes to the forger who repairs the broken spreader bars, and then paints another painting (using water soluble paint) over the Monet, so he can "return" it to the museum 3 days later. It gets more complicated when he discovers that Russo is on to him so he has a second forgery made (even the edges forged to match) over the top of "Dogs Playing Poker." He doesn't know if it will be necessary, but given his research into his new adversary, he concocts this contingency. It is likely that he has many contingencies in place, but the "Monet with a ghost underneath" is the only one we get to see. Of course for my theory to hold water, there must be (or have been) that earlier forgery - unless it has been destroyed.