New CAPTCHA

[ElbertF]

If you throw in a milti-coloured background, and possibly do the same for the letters, you might have something decent enough

I tried using a multi-colored image in the background, but it only makes the letters more readable unless they could be filled with a pattern matching the background. This way the letters would still be visible only by it's shade, as in my examples. I can't use the imagesettile() function to set the font color, that would be perfect..

[edit]

Well I've managed anyway, the letters are now transparent and only visible by it's (double) shade. I added lowercase and special characters and removed all characters that could be confusing (1, i, 7 etc.). I also added some more noise to the background. What do you think?

[MKruer]

I like the first image above the F@8fk the @8 is incredibly complex using any of the current techniques, so you are on to something there, I think that we need to use the extended character sets of @#$%&? Ones that are easily distinguishable from other characters, not that I stayed away from !^* mainly because they are too small or could be confused with other characters. Also I like the idea of mixing cases, upper and lower.

One thing I am interested in is creating a few false positives, something that the human eye would not pick up but that bot using find all edges will. This would be like a bright green letter on an equally bright yellow background. Unless you have very sensitive eyes, and or a very sharp monitor, no one in there right mind would be able to see this image. but edge detection would.

[MKruer]

BTW this is what I am talking about when I say false positive. How many people can honestly say they can read the Second Image?

[ElbertF]

You'd be better off using non-existing characters (like the ones in the background of the images above), since it easy for a computer to just ignore shapes with low contrast.

[MKruer]

Like I said, you can just throw it in. If a bot tries to use simple edge detection then it would pick up on other stuff that a human eye should not see. Besides there are cretin low contrast colors that a human can easily see, so its not just simply tossing out low contrast images. Most of the image above could be considered low contrast images.

All i did with this is adjust the hue, the luminosity and saturation has stayed the same. yet this is easily readable.

[ElbertF]

I decided to drop in some filled characters aswell.. And there is plenty of information in the back that only a computer would notice

[MISIIM]

How about a letter that a bot will see but a person will not.

[Timmer]

Hey, my first post in area51. Look at all the pretty colors.

First thought - I am so excited to see this thread. I have been following it for days. The captcha prototypes are very exciting.

I've said this before - I currently run about 8 phpBB sites and I'm getting hammered with spam registrations.

I downloaded a Perl script the other day that makes simple CAPTCHA images and I'm working on implementing my temporary solution. It works like this:

1. Replace the alphabet with symbols (the theory here is that OCR won't be able to decipher them).

2. On each CAPTCHA view, randomize the symbol names (one time "two wavy lines" is called ORT, another refresh it is called ZOD, etc.)

3. Provide a legend to the randomized names - the legend would provide a text description of the symbols. For example: "ZED is the symbol that looks like two crossed capital I characters"

4. If possible, the legend describing the names of the symbols would also be a CAPTCHA image.

5. Make the user identify 4-8 of these randomized symbols. Example: Zod Zod Ort Zod Zed.

Any thoughts on how effective this approach might be? Thanks!

[EXreaction]

How about a letter that a bot will see but a person will not.

How would you do that

[DavidMJ]

I decided to drop in some filled characters aswell.. And there is plenty of information in the back that only a computer would notice

How fast is your execution time and how much memory do you eat? Are your fonts GPL friendly? Have you considered true color fonts?