We have heard from Leanpub users that sometimes in their browser, it does not work when they try to upload an image for their profile.
If this is happening to you, here is a method that may work:
Under "UPLOAD YOUR AVATAR", click "Choose File", and select the file on your computer.
Then, click "Choose File" again, and select the file on your computer again.
Scroll to the bottom and click "Save Settings". Then, your image should appear.