The One With Rachel's New Dress - S4-E18
Continuity mistake: When Monica tells Rachel what she is cooking, and Rachel says "I really get crabby when I cook" she crosses her arms and in a flash they are on the counter again. (00:06:00)
The One With Rachel's New Dress - S4-E18
Continuity mistake: When Rachel shoos the birds into the hall, the chicken turns around and heads away from the guys' door, however when Joey opens the door the chicken is right outside the door. (00:10:15)
The One With Rachel's New Dress - S4-E18
Continuity mistake: In The One With Rachel's New Dress, she's in her underwear on the sofa when Joshua comes in. In wide shots focusing on Joshua she's quite laid back, but in close shots of her she's sitting more upright. Worse than that, her legs are crossed, but uncross in the shot of his parents coming in, only to re-cross in the next shot when she gasps. (00:14:35)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.