You are required to write signatures and descriptions for all functions, and also descriptions of all your structures. Additionally, functions must be tested, either using check-expect, or (for images) just by showing the image.
Make sure to have enough test cases to demonstrate that the function is correct. I may take points off for a lack of testing (in addition to those taken off for incorrect behavior) if your function doesn't work on particular expected data and there is no test for it. It's much better to leave a test that fails (perhaps in comments) that shows that the function doesn't work on given data and you don't know how to fix it.