Forced by the number of hits at the Dilbert pictures, I already had taken some first counter measures against hotlinking here. I've changed the scripts to prevent hotlinking in another way.

The counter measures are different this time, a little more sneakier and are described here.

Page's like this one or this one show the results.
I'm not blocking everything, I have blocked just the url's that deliver the pictures from the cartoons (Dilbert, Fifthwave, Dirkjan, Fokke en Sukke, Splinter and Userfriendly). Some other pictures are still available.
This boiles down to:
- if the url is for a picture
- if HTTP_REFERER doesn't match one of the two websites
- if the asked url is for one of the picture-directories
- then you'll get the output from showpic.php

The output from showpic.php is html, not an picture, so a browser just shows the famous broken image placeholder ( ). Whenever someone directly links to the pictures, they will get a nice html-page with the picture and a link to the original site.
I've changed the showpic.php a little, the generated ALT tag now includes the name of the picture an the url for the site.

Later I thought of something extra, something to discourage people to download all pictures from my site with a grabber. The script showpic.php now has a small delay built-in, so the downloader just has to wait a little longer.
usleep(2000000);
causes a two seconds delay. This also causes extra sessions in the webserver, but I'll just have to see if it's worth it.