Other mistake: When Phoebe and Ross are at JFK, some of the people who are at that airport are the same people who are also at Newark. It's particularly funny to see the people behind Ross and Phoebe at JFK when Phoebe claims they're on their honeymoon, and when it cuts to Rachel at Newark as she's looking for her boarding pass, those same people are there too.
Continuity mistake: When Phoebe's driving Ross to the airport in her cab the rear view mirror vanishes from the windshield, then it reappears and disappears again. Additionally, when they start their drive the cab doesn't have a side view mirror on the passenger side, but en route the cab has acquired one, then it vanishes again.
Other mistake: The photo in Rachel's passport at the airport is not of her. (00:29:45)
Continuity mistake: When the friends put down their keys, the keys' positions change when the camera pans the apartment. (00:25:30)
Continuity mistake: After Ross decides to go after Rachel, in the overhead shot all four of the cab's doors are closed, but when it cuts to Ross and Phoebe getting in and shutting their front doors suddenly both back passenger doors are inexplicably wide open, then when Ross shouts about missing seatbelts both back doors are closed again. Then when the guy gets into the back seat he shuts his door, but when he asks for the medallion number both back doors are open, and then they're closed again.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.