1. at spawn, by the Teddy Bear shadow
2. in the Fly Trap easter egg window, before entering Animal Testing
3. Animal Testing corridor, on the right hand side, in a zombie spawn window
4. Outside, by some stairs, looking through the window in the room before Double Tap.
5. In the room with the song piece, right of teleporter Z-B
6. in the zombie window, where you can see some gold ingots, teleporter Z-C (typo in video)
7. Animal Testing, before teleporter Z-A in a zombie window

https://www.youtube.com/watch?v=FJuL2W9Ag34