The One Where Rachel Tells... - S8-E3
Continuity mistake: At the start, before Monica and Chandler leave for their honeymoon, note the chairs around the kitchen table. When Rachel walks in to tell the couple to have a good honeymoon, the chair in front of the fridge and the chair in front of the stove have switched places.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.