It's not just you. Most people are having trouble with that. I'll add a hint system once the jam is over so you don't get stuck.
The clue is 2143 and you have to enter the number of corners of each of the paintings in the correct order. The first painting has 4, second has 0, third has 2 and fourth has 6, so the code is 0462
I've also mentioned the answer for the third room in one of the comments on the game page, if you need :)
Thanks for playing!