How to find the quality of a picture?

I have a Nikon D3100 and I'm doing a project to determine how light effects pic quality. How do I measure picture quality?

You don't find picture quality. You actually see it. If a photo is correctly exposed (0 Values) then it's okay. By adjusting your EV (exposure values) it will then affect light. Adding values like EV+1 to EV+3 will overexpose 1 to 3 stops and Subtracting values like EV-1 to EV-3 will underexpose the photo 1 to 3 stops.

Low or High Resolution is determined by opening the photos properties. Go to photo>right click>right click "properties." You can now see the file size. Usually small files have low pixel qualities.

Your project should have 1 normally exposed picture, 3 sample of +EV values and 3 samples of -3 values.