After setting up Bluetooth on my phone and laptop, I was faced with another problem: the phone saves images using filenames of the form ImageXXX.jpg — which is OK the first time, but tends to conflict with older files later on as the "XXX" counter restarts from 0. One may think that "mktemp" is a solution, but unfortunately that command won't let us choose the extenion of the created file. Instead, on Ubuntu and Debian, use "tempfile":

cd /mnt/Memory\ card/Images/
for f in *; do mv $f `tempfile -d $DEST_DIR --suffix=.jpg`; done

tempfile will create unique file names in the destination directory and avoid race conditions at the same time (not really an issue in this case, but good to know.)

Update: here's a different method that will generate more meaningful (though not random) names

t=`date -u '+%F_%H-%M'`
for f in *; do cp $f $DEST_DIR/${t}_$f; done

The files will be prefixed with a timestamp, which is probably more useful.