I have a couple of key ring photo frames intended for research into DR in case any customer wanted one recovered... Ok that's the story I tell when I want to hack a device .. I am guessing you are talking about the 7" ones and the like? I have some of those too..
If you get me sidetracked into having some fun with these there will be trouble!
I expect that these devices would have an embedded Linux OS. If so, then there may be a way to telnet into it via a serial port, or perhaps there is a JTAG port.