Watermarking for my photos. Run like `./watermark.sh input_file.jpg`, which produces `input_file_wm.jpg`

watermark.sh

#!/bin/bash
if [ "$1" != "" ]; then
	dr=$(dirname $1)
	scdr=$(dirname $0)
	fn=$(basename $1)
	filename="${fn%%.*}"
	extension="${fn#*.}"
	output="${dr}/${filename}_wm.${extension}"
	# wm.png is my watermark. It's a white logo with 50% opacity and a transparent background.
	wm="${scdr}/wm.png"
	echo Generating watermarked version of $1 under $output...
	composite -dissolve 100 -gravity southwest $wm $1 $output
	echo ...Complete
fi