My first thoughts for the word confined was a bird in a cage, but I thought that would be good to think past the first thought for something different so I started jotting down words that confined made me think of. I ended up with the idea of private school girls who all have to wear the same uniform. I am sure they feel confined at times! I would.
The below version is one outlined in pen - I think I like the sketchy pencil one above more.