Easy steps to add a digital watermark to image with GIMP

1. Download watermark plug-in (watermark.scm) for GIMP here.
2. Go to your home folder and enter key Ctrl+H to view hidden files (or go to  File Browser (Nautilus) menu, and select View -> Show Hidden Files).
3. In your home folder Go to /.gimp-2.6/scripts directory folder and drop watermark.scm to that folder.
4. Open GIMP (Applications -> Graphics -> GIMP Image Editor).
5. You will see Script-Fu menu has been added to your GIMP menu.
6. Open image file.
7. To add digital watermark go to menu Script-Fu -> MyScripts -> Watermark. Script-Fu: Watermark window will open.

8. On Script-Fu:Watermark window you can enter your watermark text, choose font type, font size, location to put watermark text on your image and opacity for watermark text. After finish click OK button.

9. Now your image has been added digital watermark. Don't forget to save your digital watermark image.