You need to install the Python Imaging Library (PIL), which is a 3rd party module. I think SimpleCV is supposed to install PIL as part of the overall installation process, but PIL is one of those weirder programs to set up.
Try typing in the following from the command line:
pip install pil
Alternatively, you can install using the binary.
If that still doesn't work, try installing pillow, which is a friendlier and actively-developed fork of PIL:
pip install pillow