With the pointer on the picture (it will look like a little bullseye), hold down the button on your mouse and move the cursor around in any direction to look at various perspectives of the picture.

Mac owners: to zoom in, let go of the mouse button and hold down the shift key; to zoom out, hold down the control key.

Windows people: to zoom in, let go of the mouse button and hold down theshift key; to zoom out, hold down the control key.

You can move via the arrow cursor keys as well.

The mouse pointer has to be somewhere on the picture for the zoom functions to work.