The Haar face detection example in Image Processing Toolbox provides an option to run the detection on a smaller Region of Interest rather than the complete image. This can be done by modifying the macros
ADI_ROI_IMAGE_WIDTH, ADI_ROI_IMAGE_HEIGHT, and updating the variables X_OFF, Y_OFF macro in demo_application_haarfeatures.c at line 426.
However using this Region of Interest seems to miss detecting the faces which were earlier detected when the detection is run on the complete image. Is there a problem with using the Region of Interest for detection?