Select the photo you want to zoom into and switch to the "Move" tab in the media pool. You will be in the "Camera movement" sub section. This is where you can set up more customized camera panning and zooming. Just click on the zoom in icon (the rectangle with the plus sign on it). A rectangle will appear on your photo in the preview monitor. You can adjust the size and position of this rectangle to specify the exact section of the photo you want to zoom into.

I hope this helps.