Joakim

Erdfelt

Want to watermark your images in an automated fashion using command line tools?

The Technique

Prerequirements:

• Unix: Use of a POSIX compatible Unix is required. Linux, OSX, FreeBSD, etc... are all good. If you are windows user, go install a copy of Cygwin, it's a POSIX compatibility layer on top of windows.
• Bash Shell: If you have Unix, you most likely have Bash already.
• ImageMagick: Install a copy of the ImageMagick tools, using your favorite installer (yum, apt, rpm, deb, tarball, source, etc...)

Start with by creating a PNG image with alpha channel that represents the overlay that you want.

watermark.png (219x42)

Use the composite tool from ImageMagick to apply the watermark.png image onto the original image to produce the desired effect.

$ composite -gravity SouthEast watermark.png original-image.png output-image.png

Here's how to take a directory full of PNG files and add a copymark to each.

for PNG in *.png
do
  echo Adding watermark to $PNG
  composite -gravity SouthEast watermark.png $PNG ${PNG//.png}-watermarked.png
done