[TuringNYC]

The first question has been widely answered, so let me jump to the second question -- bounding boxes.

In the past, some people did this inefficiently by just sliding a window across the image and using the same classifier you'd use for the first problem. But this is inefficient, and different sizes make it more inefficient. So the best solution is to use an "Object Detection" network, look into SSD or YOLO to see an example of this.