Plot hole: In TOW Ross tells Rachel he cannot see her following a promise to Emily, the rest of the friends go into Monica's bedroom. Joey hauls out a box from under the bed, saying that he's been hiding it there since Ross said the wrong name at the wedding. Surely Monica, with her obsession for keeping the place clean, would have noticed a box under her bed? (00:04:10)
The One With The Ride-Along - S5-E20
Plot hole: When Rachel picks up the box of photos they all fall out, because the box isn't sealed with tape or even folded properly. But there's no way for that to have happened. Monica would have brought the box from somewhere and put it on the couch, and the photos would have fallen out then, and she would have fixed it (this is Monica, after all.) The only way for this to have happened is if she put the empty box on the couch, unfolded/unsealed, and then put photos in it - which Monica would not do.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.