[Christophe_O]

Originally Posted by steadicamop

...I think I may up the total number of images to 20, just so it's an option anyone can use...

Well I am no expert but here is my thinking.

• I suggest to create 2-3 multiple-choice options instead of just one. I.e., the verification page might consist of 2 or 3 challenges to choose the correct image from a row of 7-10 images. The visitor could be asked to check a box beside the correct image, 2-3 times. Still simple for humans, and only requiring a download of 14 to 21 images, but offering 49 to 343 possible answers.
• Otherwise, I am concerned that this hack may not work if it becomes widely used. To be human friendly, we need to limit the images to 15 and also to allow 3 tries. This allows a high guessability ratio of about 20%. Even with 30 images, but only 1 question, it's still not ideal for blocking robots, and less human friendly. Currently 15 images can work fine because this is not widely used. But if this program becomes popular, it will also become worthwhile to program robots to get in by repeated guessing--going to the next forum on the list, then returning the next day, or etc--unless the variation is increased.
• Also, when I click a 'wrong' image ... then try to go 'back' with Firefox ... the images are not refreshed automatically. This will confuse some people, I think.
• Very promising hack! Has my vote for MOTM. Sorry I accidentally left my original comments in your old thread: Enhanced Image Captcha 1.11