I hope this is the official PIL development repository... PIL homepage is light on details. Anyway...
On some palette-based PNG files, an error is raised, e.g.
ValueError: invalid literal for int() with base 10: '\xff'
This is caused by the following line in getcolor() in ImagePalette.py:
self.palette = map(int, self.palette)
which should be
self.palette = map(ord, self.palette)
After coming up with the potential fix, I looked around and found it implemented in some PIL forks out there (and even mentioned in the official mailing list as a fix for this bug) - but unfortunately it's not yet fixed in the official PIL.