Sebastian Kirsch: Blog

Saturday, 12 February 2005

Gerhard Richter exhibition in Düsseldorf

Filed under: — Sebastian Kirsch @ 14:05

A Gerhard Richter exhibition opens today in Düsseldorf at the Kunstsammlung Nordrhein-Westfalen. The exhibition is open till May 16th.

AuthImage: CAPTCHA! Gotcha!

Filed under: — Sebastian Kirsch @ 13:55

I added CAPTCHA support to my blog now, to curb blog spam. A CAPTCHA is a kind of reverse turing test: It is intended to allow humans to access a certain function, but keep out automated programs. (For example programs that deposit spam in the comments section of a blog.) Nowadays, this is usually done with an image that contains a short word, or a some characters, but twisted, distorted and with a distracting background. This is an attempt to foil OCR (optical character recognition) programs.

I used the AuthImage plugin for Wordpress, by Gudlyf. The installation was relatively straight-forward, but I had to make a couple of changes:

  • authimage-inc/image.veriword.php: This file used the tag <? to introduce PHP sections instead of the more common <?php; this prevented my web server from processing it properly.
  • authimage-inc/class.veriword.php: I added cache control headers to the outputImage method to prevent caching of the image.
  • The README.txt file mentions wp-comments.php and wp-comments-popup.php as places where to add the CAPTCHA section, but forgets wp-comments-reply.php.

I also added a short explanatory text, explaining how to get a new image if you can’t decipher the current image, and that a comment with the wrong code will still appear on the web site, it may simply take a while. This way, people who enter the right code get instant gratification, and those who can’t decipher the image will still get their comment posted. (And the CAPTCHAs from this system can be really hard.)

A short anecdote from the history of CAPTCHAs: A couple of years ago, German email provider web.de had a free SMS gateway. They tried to limit abuse of this system by providing a simple CAPTCHA: An image with a word (without distortion or background noise) that one had to enter in order to send the SMS. It turned out that this system could be defeated with a 60-line shell script, using lynx and the free OCR system gocr. The complete details are here.

Still more of the same theme

Filed under: — Sebastian Kirsch @ 00:54

Three weeks ago, I remarked that all the books I was reading at that time seemed to be about mental illnesses.

Well, I went to the bookstore today to pick up a few novels. I had just finished my seminar and felt in the mood for buying some light reading to distract myself. And promptly, I gravitated towards The Curious Incident of the Dog in the Night-Time by Mark Haddon. After finding out that the protagonist is suffering from Asperger’s syndrome (which is a mild form of autism), I put it down again – and picked up Will Self’s Dr. Mukti. Reading something about psychoses on the cover, I put that one back as well.

And I already have Andy Behrman’s Electroboy on my amazon wishlist, which is about manic depression. (Behrman has also been nicknamed “the real American Psycho".)

As this theme of mental illnesses keeps reoccurring, perhaps I should just give in and reserve one bookself for my “psychotic department". And try to read the books one after the other, just not four of them at the same time.

What did I buy in the end? I did find something lighter: The Well of Lost Words by Jasper Fforde. My bookstore was offering a pack of three of Fforde’s books for €14.80, but I chickened out and bought just one of them. That probably means that I’ll pay more for the other two …


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