Add watermark to file

gistfile1.txt

#!/bin/bash

# needs imagemagick
set -e

help() {
  echo "Adds a watermark text to an image. Generates a new image file with the given watermark."
  echo "Usage: $0 <source> <destination> <watermark> [size]"
  echo -e "\tsource: The original image file which the watermark text will be added to."
  echo -e "\tdestination: The generated image with the watermark text added."
  echo -e "\twatermark: The text that will be added as a watermark to the image."
  echo -e "\tsize (optional): The text size. Defaults to 80 if not informed."

  exit 1
}

if [ "$#" -lt 3 ]
then
  help
fi

SOURCE=$1
DEST=$2
TEXT=$3
SIZE=${4:-80}

convert -density 150 -fill "rgba(255,0,0,0.25)" -gravity Center -pointsize $SIZE -draw "rotate -45 text 0,0 \"$TEXT\"" "$SOURCE" "$DEST"