gtkam with USB mass storage camera

I've been trying to use the gtkam camera program with my digital camera (a Toshiba PDR M25). The camera interface simulates a mass storage device, and I can retrieve the images perfectly well using /dev/sdb1 (or /media/sdb1, the mount point). However, I cannot get gtkam to recognize the camera (and gtkam provides some handy facilities such as thumbnails). If I use the "add camera" function, I get "no camera detected", and if I try to specify the camera as "USB PTP Class Camera", the only plausible choice, I get the message "Could not list folders in `/'". (The other Toshiba cameras don't work either.) Any suggestions about how to get gtkam to recognize the camera? Paul Abrahams