Some e-mail providers now offer a spam filtering service requiring the sender to visit a webpage and enter a word from a picture on the screen to confirm their message. The picture is displayed in a way that makes OCR programs not able to interpret it and therefore eliminate non-human replies.

An Ishihara test is one for color blindness. Several mixed color dots are listed and depending on the viewers ability to see all colors, different letters or numbers are seen.

The Ishihara spam filter will test for both. Depending on the viewer's ability to see all colors, the words they'll see in the challenge picture will be different. Depending on the word the viewer enters to proceed, the filter can both let the message pass, and inform the user that they're red-green colorblind at the same time.
-- Mr Burns, Nov 23 2004

Ishihara color blindness tests http://www.toledo-b...blind/Ishihara.html
[Mr Burns, Nov 23 2004]

mixedcolordot.com is available - you could sell it from there.
-- thud, Nov 23 2004


Sure, why not? I need to be reminded of my defects as frequently as possible.
-- half, Nov 23 2004


That's what I was thinking too, [half], but I didn't want to elf-identify. I hate those little dot patterns and I hate the doctors (DOCTORS!) who always react with amusement and disbelief ("Hee haa hee, you mean you can't see the 57? It's right there!") when I don't see the damned numbers. {pant, pant, pant/rantrantrant}
-- contracts, Nov 23 2004


Maybe those of us with different hue determination abilities could see a different message? Tell the email service which colours you have a problem with, and it will convert all spam and ads to a format where they are invisible. That way the advertisers can put their hand on their heart and say their adverts always get through to the punters, while you don't actually have to be bothered by their nasty little commercial messages.

Since I am not colourblind, I dunno how it all works, but I suspect my suggestion is a tad too simplistic. :-)
-- moomintroll, Nov 23 2004


Finally, a solution to the growing problem of colorblind spammers.
-- waugsqueke, Nov 23 2004


Yes, we can kill two unrelated birds in different trees, one of which doesn't need killing.
-- wagster, Nov 23 2004


green/red
-- reensure, Nov 24 2004


As an optometrist, I approve. +
-- vigilante, Nov 24 2004


Surely this could be combined with Rorschach inkblot tests to catch colourblind spammers with sociopathic tendencies. (Or to stop people who think everything looks like a fluffy bunny from emailing you.)
-- pottedstu, Nov 24 2004



random, halfbakery