If you have a fuzzy profile picture, then it's probably because the original image was too small. When the uploaded image is too small, it will blow up the image to fit the window and make it look fuzzy.
Try to use a square image that is at least 100 x100 pixels to ensure the best image quality. The image that you upload will be re-sized to 100 x 100 pixels. If your image is taller than it is wide, then it will be cropped to be a square.