i got a questionnaire with check boxes inside. now i would like to match a template of the questionnaire and filled out questionnaire (out of my webcam)... i already did a template matching to find the questionnaire in the webcam image and did a back transformation to the original template.. now my problem is, how to find the checks inside the questionnaire? if i am using image subtraction (template image – webcam image) and corner detection, i still have noise inside, because the images are not perfectly matched (1-5 pixels shifted).. is there a better way to subtract images? the other issue is that I still will find non-crosses (e.g circles, chrossed-out crosses) any idea?