You need to find the painting that belongs here, though you won't know why until you need to deal with all the paintings.
What am I supposed to do with all these paintings?
What you're looking for is a roll of canvas about two feet wide, old and dark. Keep your eyes peeled for something like that.
If you don't see it, look in the tool room --
-- on the right side of the table where you assembled the battery, next to a thing that looks like an old scale. Once you have it, click it on the empty frame to put it back.