I thought this as well. However, the time periods during this section of the movie are quite sketchy.
It isn't so much the fact that he puts it *in* his brief case in the scene prior, but that he takes it *out* of a brief case in this scene.
Quite frankly, it would be safe to assume the painting he took out of his briefcase is not the stolen painting, but the poker playing dogs with the copy over top. It is doubtful, from the later mentioned time period of two days, Mr. Crowne ever brought the Monet home. When he toasts the picture, he is most likely toasting to Anna's work - not his own. It is not like Crown to gloat or celebrate.
The point is that a $100,000,000 Monet painting on a wooden frame was easily 'folded' into a briefcase - this would be difficult at best and would surely damage a VERY expensive painting.
The Monet is an expensive painting, and it was probably damaged in the crime, but it is not the painting he takes out of his brief case when he is in his home. In fact, the painting he takes out shows the crease of the case when he opens it, and has some warping to the canvas as he puts it in its hiding place. This was just not a slip-up.
If you people did your homework before critisizing the movie you would find out that the director had constructed an elaborate explaination for the folding of the painting and its seeming unflawed appearance. But he left this out because he thought it would make the audience feel like he thought they were stupid so he left it out and hoped that the few people who noticed didn't whine so much.
This is to WD. Even if the picture he takes out of his briefcase is the poker playing dogs, you'll notice as he goes to place it in the hiding spot, it has a wooden frame on the back. It doesn't matter if it's the original, you cant fold a wooden frame.