The One Where Ross Moves In - S5-E7
Revealing mistake: When Joey and Chandler go in the bedroom to talk, Joey suggests they play a game of foosball. There is no ball when they start playing - quite noticeable when Joey " scores" a goal.
The One Where Ross Moves In - S5-E7
Revealing mistake: During Danny's party you can see Monica's apartment through the gap between the door and the wall, despite the party taking place on a lower floor. This is because they just reused the set for the hallway to save having to build a new set for the "lower floor."
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.