The One With Joey's Dirty Day - S4-E14
Continuity mistake: When Rachel is asking Ross if he will take Emily to the opera, the amount of biscuit in his hand changes throughout. (00:06:15)
The One With Joey's Dirty Day - S4-E14
Continuity mistake: When Rachel is telling Monica and Phoebe about her night out with Joshua the previous evening, Monica is holding a glass of orange juice. To begin with the glass is half full, but then changes to being almost full to the top, and then back to half full. (00:09:00)
The One With Joey's Dirty Day - S4-E14
Continuity mistake: In the scene where Mr Heston confronts Joey about using the shower, Mr Heston points at Joey from a seated position. As the shots switch Mr Heston's "pointing" hand also switches. (00:16:30)
The One With Joey's Dirty Day - S4-E14
Continuity mistake: After Chandler gets back from the strip club, when he throws his jacket and scarf they both land on the rug between the recliner and coffee table, but when Chandler sits in his recliner the jacket is gone and the scarf is lying on the floor on the opposite side of the table.
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.