Install ImageMagick

sudo apt-get install imagemagick

Prepare your working environment

Make a directory to store the watermark image (~/Pictures/watermark) and photos you’re working on (~/Pictures/temp). Copy the watermark image and original photos to their respective directories.

mkdir -p ~/Pictures/temp/
mkdir -p ~/Pictures/watermark/
cp /path/to/watermark.jpg ~/Pictures/watermark/
cp /path/to/original-photos/*.jpg ~/Pictures/temp/

ls -l ~/Pictures/watermark/
-rw-r--r-- 1 gmendoza gmendoza 3311 2007-12-30 17:35 watermark.jpg

ls -l ~/Pictures/temp
-rw-r--r-- 1 gmendoza gmendoza 885788 2007-12-30 17:35 ubuntu1.jpg
-rw-r--r-- 1 gmendoza gmendoza 128922 2007-12-30 17:31 ubuntu2.jpg

Change directories to begin working on your photos.

cd ~/Pictures/temp/

Resizing with “convert”

Let’s say you want to specify a maximum width of 440 pixels (height being adjusted proportionally) in order for you to post the images appropriately within the specifications of your website borders. The syntax would be the following:

convert -resize 440 original-image.jpg new-image.jpg

In this example, we will specify the same name for the output files, which will overwrite the original copies.

convert -resize 440 ubuntu1.jpg ubuntu1.jpg
convert -resize 440 ubuntu2.jpg ubuntu2.jpg

Watermark with “composite”

You will probably want to watermark the images after they have been resized, this way there is no distortion of the watermark, and it is appropriately sized. In this example, we will also set the watermark transparency level to 15%, and overwrite the original file again.

composite -gravity northeast -dissolve 15 ../watermark/watermark.jpg \
ubuntu1.jpg ubuntu1.jpg
composite -gravity northeast -dissolve 15 ../watermark/watermark.jpg \
ubuntu2.jpg ubuntu2.jpg

Your photos will now have a nice watermark in their upper right hand corners.

Automating the process with a script

You can automate these steps and apply them to a large number of files using a script of course. Feel free to download this one and modify it to your liking.

http://www.savvyadmin.com/downloads/watermark.sh

#!/bin/bash
WATERMARK="$HOME/Pictures/watermark/watermark.jpg"
 
echo "*****************************************"
echo "* Image Resize and Watermarking Script  *"
echo "* By Gilbert Mendoza -  SavvyAdmin.com! *"
echo "*****************************************"
echo " "
 
for each in ~/Pictures/temp/*{.jpg,.jpeg,.png}
 do
  echo "Working on "$each" ..."
  convert -resize 440 "$each" "$each" >> /dev/null
  composite -gravity northeast -dissolve 15.3 $WATERMARK "$each" "$each" >> /dev/null
  echo "... Done!"
 done
exit 0

Additional Options

Please check out the ImageMagick website for more information on the many options and features their products have to offer.

http://www.imagemagick.org/script/command-line-processing.php

http://www.imagemagick.org/script/command-line-options.php

http://www.imagemagick.org/Usage

Related posts:

1. Fixing Dates in Image EXIF Tag Data from Linux