Hi Taheri,
It is possible that the OS has exposed a framebuffer device at /dev/fb0. It's possible that it acts as an overlay to the camera image or in other words as an OSD. You can check that by doing this from the console:
cat /dev/urandom > /dev/fb0
then you look at your screen and if the image is all noisy but the camera image is still visible under the noise that means that you can use it to solve your problem.
write back if this experiment works~!
best regards
