have a set or resulutions (width*height) applied to your camera.
camera.setMode(width, height, thirdParam);
if they are supported when reading bagck camera with and height it will be the same as the value you passed in then called set mode on the camera.
Well thanks for the fast reply, I have tried that already. With Apple iSight Camera in my macbook, which does not support HD i have set the capture resolution to 720p by camera.setMode(1280, 720, 90) ..... and when i get the width and height of the camera using it was 1280x720.... when i am sure that iSight does not support 720p capture.