The One with All the Poker - S1-E18
Revealing mistake: When Rachel is doing the shuffling trick, it is clear that it is a trick deck. The cards, whilst flying from one hand to the other, change the angle of flight in mid-air, and some of them even move backwards as she moves her hands further apart from each other. This could only happen if the cards were connected to each other. (00:13:20)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.