I picked one up for $3 from OfficeWorks and wanted to put pictures on it.
So… I could list (and get) the default photos with gphoto2 (shipped with Fedora 20 it just worked): gphoto2 -L (list), -P (get all).
It turns out that the images are 128×128 PNGs! Easy: change resolution in GIMP of a picture I want, and then “gphoto2 -u filename.png” sent it to the device.
Wheee, it works! Not bad for $3