Resize with watermark

resize.sh

#!/bin/bash
# author jsteiner
#
# Resizes an image and adds a watermark. To customize which watermark is added,
# edit the $WATERMARK variable below.
#
DIR=`dirname "$BASH_SOURCE"`
WATERMARK="$DIR/watermark.png"

SRC="$1"
DIM="$2"
DEST="$3"
DEST_FILE="$DEST/$1"

if [ $# -ne 3 ]; then
	echo "invalid number of arguments supplied"
	echo "usage: `basename $0` <source_file> <dimensions> <dest_dir>"
	echo "where:"
	echo "        <source_file>       is an image file"
	echo "        <dimensions>        dimensions of new file, for example:"
	echo "                            1280x720, or 1280x, or 720x"
	echo "        <dest_dir>          output dir in which a new directory"
	echo "                            called 'resized/' will be created"
	exit 1;
fi

if [ ! -f "$SRC" ]; then
	echo "error: source file $1 does not exist"
	exit 2
fi

if [ ! -d "$DEST" ]; then
	echo "error: destination $DEST is not a directory"
	exit 3
fi

if [ -f "$DEST_FILE" ]; then
	echo "error: destination file $DEST_FILE already exists"
	exit 4
fi

# first resize the file, then apply the watermark. miff:- makes piping available
convert "$SRC" -resize "$DIM" miff:- | composite -gravity southeast -geometry +10+10 "$WATERMARK" miff:- "$DEST_FILE"