Gary, please review additional comments too. I'm not sure if my thinking is
If you are downloading images from the web, who knows what you are getting
for dimensions? After all, the pictures are likely cropped by someone else
Anyway, don't use the Crop tool. (It's name is deceiving when you are
specifying images sizes. It really should be called Crop/Resize because it
will resample your image to the size you indicate in the "width / height"
fields. Not good--especially if you're doing a heavy crop).
That said, I would press M for the marquee tool (rectangle), ...