What programming code are you using.
Others with more expiance reading from a device rather then a file would probably be more helpfull then me but in C you would want to open the file as readonly. example code
cameradata = fopen("/dev/video0","r");
/* You would probably want to only grab a assiened amount of data
from the camera or however the assoicated driver works */
more then likely there is something more complicated your going to have to do like passing information back to the camera to make it grab a picture and transmit it back in a understandable format. Ive never done complicated programs like this before so im kinda in the dark. Mabye somone else here has an idea.