Mike Driscoll is in the process of writing a new book titled “Pillow: Image Processing with Python” Funded with Kiskstarter.
While it is not a photographic book it should provide a really good introduction to some of the image processing possibilities using Python & Pillow (both Open Source). Mike writes in a very approachable style (see his blog Mouse Vs Python to get an idea or the free preview of the first 3 chapters using this link.
The Kickstarter campaign has finished but the book can be purchased on Leanpub: https://leanpub.com/pillow/ and will doubtless be available via other channels.