Dynamic watermarking of hotlinked images?

I run a wallpapers website and some people hotlink the images, I don't want to stop the hotlinking all together but I think it would be nice to have a watermark on each image. I don't want watermarks to be displayed on the images if they're being viewed from my domain but if they're being hotlinked I want a watermark to display.

I know you can add a watermark to an image with PHP but is it possible to do this dynamically with htaccess on hotlinked images?

 

this CGI script looks like it does it
http://beesbuzz.biz/code/web/watermarking_hotlinked_images/

 

Looks like a good find, now I need to work out how to use cgi.

 

yup, on a hotlinked image, passed it to a script first which place the watermark

let say an image of abc.jpg is being hotlinked.

your htaccess will redirect it to addmywatermark.php?image=abc.jpg

on your addmywatermark.php

add the code to place your watermark on images.

 

why not use in all your websites with watermark? i see a lot of graphic-cartoon-picture sites that had watermark in all of their pictures.

 

wouldn't that ruin the layout?