How can I define whole images as ROI for trainCasca​deObjectDe​tector in Matlab2014?

Hello all, please help me to solve this problem. I want to train standart Viola classifier by trainCascadeObjectDetector function in Matlab. I have positive images, and each of these images are ROIs. How can I label these images for trainCascadeObjectDetector as ROI without mannually going to Image Labeler app and secting each of thaem as ROI? because there are actually thousands of these images. Appreciate any help. Thank you.