The One Where Ross and Rachel...You Know - S2-E15
Visible crew/equipment: When Rachel's talking about when Richard kissed her when she was a little girl, you can see the boom mic above her head. (00:16:10)
The One Where No One Proposes - S9-E1
Visible crew/equipment: At the beginning when they're looking at Emma between shots you can see a Cameraman or Camera in the Window.
The One With Rachel's Phone Number - S9-E9
Visible crew/equipment: In the scene where Chandler pretends that he just got home from Tulsa and meets Joey who is waiting in the hallway outside the apartment, the camera cuts between Chandler and Joey. Every time the camera shows Chandler, there is a wooden wall at the left edge of the screen with an orange tape. This is evidently part of the set, because when the camera cuts to Joey, the wooden wall with the orange tape is nowhere to be seen. (00:16:45)
The One Where Nana Dies Twice - S1-E8
Visible crew/equipment: When Monica and Ross meet up with their parents and their nana, a boom mic is visible at the top of the screen. (00:04:20)
The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Chandler runs into the apartment to say Underdog has gotten away, a crew member can be seen reflected in the sun shaped mirror behind him walking through the back of the shot. It can't have been Rachel, Monica, Phoebe or Joey because Joey is sitting down and Rachel, Monica and Phoebe are nowhere near the mirror. (00:14:05)
The One With The Embryos - S4-E12
Visible crew/equipment: In the shot where Monica suggests that Ross creates the questions, there is a red boom mic followed by a blue boom mic at the top center of the screen. (00:05:15)
The One With The Soap Opera Party - S9-E20
Visible crew/equipment: After Ross introduces Charlie to Phoebe and Monica in Monica's' apartment Charlies' cell phone rings. She turns around and in the back where the "secret closet" is, you can see on the left corner two spotlights.
The One With Chandler In A Box - S4-E8
Visible crew/equipment: Just as Ross asks Rachel for the necklace he got her, a stage light is very visible above the bathroom door. (00:12:35)
The One With All The Kissing - S5-E2
Visible crew/equipment: When Rachel tells her date she's going to have to take a rain check and goes back into the apartment, as she opens the door you can see a cameraman standing inside the apartment. (This is only visible in the broadcast version, not DVD or widescreen). (00:10:45)
The One Where Rachel Has a Baby, part 1 - S8-E23
Visible crew/equipment: Right after Rachel says, "Do you know that feeling when you're trying to blow a Saint Bernard out your ass?" the camera cuts to a view of Monica and Chandler. Behind Monica and Chandler, part of the set is visible, along with a man on crutches.
The One With Monica's Thunder - S7-E1
Visible crew/equipment: When Monica says she's opened the door to the past, a little bit of a stage light is visible above her head.
The One With Joey's Fridge - S6-E19
Visible crew/equipment: In the scene where Rachel introduces Sebatian to Chandler, Monica and Phoebe, there is a visible boom mic at the top of the screen in the wide shot, right after Chandler says, "Turns out he is kinda funny".
The One With The Embryos - S4-E12
Visible crew/equipment: Near the beginning of the show when Joey asks them who's going to ask the questions a boom mic is visible over Monica's head. (00:05:05)
The One With The Secret Closet - S8-E14
Visible crew/equipment: When Chandler walk in Joey's apartment and say "Rachel's all moved out, huh?" as he walks towards Joey a lot of set lights are visible above their heads. (00:18:55)
The One Where Ross And Rachel Take A Break - S3-E15
Visible crew/equipment: When Ross is on the phone to Rachel, near the start, just as he walks into the living area, a stage light is visible above him (only visible in fullscreen version). (00:06:10)
The One with the Monkey - S1-E10
Visible crew/equipment: When Joey the Elf deliberately jingles his elf shoes, Chandler's head may explode because of all the unspoken mocking jokes. It then cuts to a shot of Marcel, and the trainer's hand is visible in the bottom left corner of the screen. (00:07:25)
The One With The Apothecary Table - S6-E11
Visible crew/equipment: When Rachel and Phoebe are talking in front of the Pottery Barn window, a wooden set wall covered in several signs is visible on the far right in the shots of Rachel.
The One with Two Parts: Part 1 - S1-E16
Visible crew/equipment: When Phoebe knocks on Joey's door you can just see 2 orange T markers on the floor. (00:22:10)
The One with the Sonogram at the End - S1-E2
Visible crew/equipment: Ross stands up to tell his parents about what has happened with Carol. When he does he walks round the table and stands under a very visible boom microphone. (00:12:05)
The One Where Underdog Gets Away - S1-E9
Visible crew/equipment: When Joey walks into Central Perk after the VD poster montage, a tape marker is visible on the floor behind Chandlers spot on the sofa. (00:10:40)
Answer: The painting doesn't have a name, and if it does it is never mentioned in this episode.