Yes, you could do this with PowerPoint, but it won't do as good a job as the
photo editors you're using already.

In PPT, you'll need two copies of each picture. Use Insert|Picture|From File
to insert one, then select it, hit Ctrl+C to copy, and Ctrl+V to paste.

Select one of the pictures on your slide, and the picture toolbar should
show up. If it doesn't, go to View|Toolbars and select Picture to turn on
the picture toolbar.

Then use the crop tool on the Picture Toolbar to crop to the head. Do the
same to crop to the body on the other picture.

The cropped areas remain available (just turn on the crop tool and drag the
photo edges in the opposite direction) until you use "compress pictures" on
the Picture Toolbar.