You also have an approach to image processing based on "standard" scientific modules: SciPy has a whole package dedicated to image processing: scipy.ndimage. Scipy is in effect the standard general numerical calculations package; it is based on the de facto standard array-manipulation module NumPy: images can also be manipulated as array of numbers. As for image display, Matplotlib (also part of the "science trilogy") makes displaying images quite simple.
SciPy is still actively maintained, so it's a good investment for the future. Furthermore, SciPy currently runs with Python 3 too, while the Python Imaging Library (PIL) does not.