Yes it should be easy to do..
The existing example uses PiCamera to save the photo and it is then read in using the commands on this page
. You could just remove the code to take the photo and replace the "selfie.jpg" with the name of the photo you want to use.
You may have to convert the photograph to a lower resolution since the software is expecting a photo that is only 80x60 pixels. You could either do this with some photo editing software manually or use skimage
to resize it automatically