How do I take a steathy picture with my iSight camera from the command line?
Use imagesnap. It can be installed with brew install imagesnap or by downloading the binary from the website.

One use for it is to take series of snapshots:

while :; do
    imagesnap ~/Desktop/$(date +%y%m%d%H%M%S).png
    sleep ${1-1}
done


It doesn't crop images horizontally either. (Photo Booth changes the aspect ratio to 3:2.)