You can pick a profile picture from your Photo Library or capture with your camera, then move and scale it until you find the best fit.
This Swift app implements a UIImageView within a UIScrollView, and involves cropping and scaling functions.
The following GIF demo show the user signed in, a photo is picked, then moved and scaled. Later the photo is removed and replaced by a placeholder photo.
This GIF demo show a second photo was picked to replace the placeholder, and then moved and scaled to the best fit.