The One With The Girl Who Hits Joey - S5-E15
Continuity mistake: The frosting on Ross's mouth changes between when someone says "who cut Howard's cake" and "3b". (00:16:00)
The One With The Girl Who Hits Joey - S5-E15
Other mistake: When Ross and Phoebe are eating cheese puffs and party mix out of the bags, Phoebe's bag reads "Heez-I" instead of Cheez-It, and the brand "Sunshine" has been covered.
The One With The Girl Who Hits Joey - S5-E15
Continuity mistake: When Phoebe gives the housewarming gifts to Ross and also when Ross opens the door for the neighbor, his apartment number is "3B" and his neighbor's door is "3A," but in episode 14, "The One Where Everybody Finds Out," the door can be seen three times during the episode, and the number is "201" each time.
The One With The Girl Who Hits Joey - S5-E15
Continuity mistake: When Ross tells Chandler and Rachel that he's running out to buy name tags for his party, in the next shot the water bottle beside Rachel does not have its cap on, but it cuts to Rachel's closeup and the cap is on. Other differences can be seen as well, such as Rachel's hair and an extra utensil.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.