If you are taking a photo directly in the app and it is zoomed in to tight, try holding the camera further away so that your headshot is centered and there is plenty of space on either side.  The app will try and find the center of the photo, and crop a square avatar from the center.  Also, make sure you are using an image file such as a .jpg or .png if you are trying to upload a photo.  If you can’t get the perfect pic, remove your photo and add a photo at Gravatar using your email address and the app will use that instead.