tokens: In our study , we primarily focus on four recent object detection systems : the Faster R - CNN * ren2015faster , the You Look Only Once ( YOLO ) * redmon2016you , redmon2016yolo9000 system , the Region - based Fully Convolutional Networks ( R - FCN ) system * dai2016r , and the Single Shot Multibox Detector ( SSD ) system * liu2016ssd .