It seems you won't be able to copy the files via USB. (I never really figured out what kind of logic/magic is going on there).

Instead I'd try to get the files off the device another way - either by copying them to a µSD card or via some sort of network connection (e.g. an sshfs mount).
Then you can run the file command on each of the files to determine their magic blocks, which will give you an output like this:Now I know "somefile" is a jpeg picture, so in the best case I can just rename it to "somefile.jpg" and open it with any picture viewer.