[ Thanks to An Anonymous Reader for
this link. ]
“I’ve written two versions of this script. The
first one I’ll show overwrites all of the images in a
directory with the watermarked images. This should be done with
some degree of caution as there is no way to undo the changes
unless you have the files backed up. Save the following script in
your ~/bin/ directory and name it wm-ow.“The second version of this script will not overwrite your
images. It will create a new file with _wm inserted into the file
name. This is the version you should use if you’re not sure
about what settings to use in the script. Save the following in
~/bin/ as wm-new.”