I would suggest submitting one image per piece for the majority of your works, and include a couple detail shots for your strongest pieces. Remember that the admissions committees will be looking quickly through images from many applicants, and they want to get the gist of your work first, and go into detail only secondarily, if they already like what you're doing and are interested in your application as a whole, with your statement, etc.
One thing that I've noticed is now that most schools use slideroom, they let you uploade really high resolution images. So take advantage of that, get good photos, and they will zoom in if they are interested. Reserve detail shots for alternate angles and other aspects of your work that are really not legible from a single image.