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The Next Big Thing in CAPTCHAs (catchmyfame.com)
11 points by edw519 on Oct 15, 2009 | hide | past | web | favorite | 22 comments

This looks trivial to defeat by simply comparing the top and bottom edges of each image, and picking the combination with the best fit. The faces might fare a little better under that test, but the logos and colourful shapes would likely be successfully matched every single time.

Indeed. This is absolutely trivial to defeat, and anyway the space of possibilities is just too narrow. Even with faces, the amount of similarity between top pixels of the middle row, and bottom pixels of the top row, are a lot bigger when there is a match.

Actually, logos are the harder of the pair. My simple attempt only gets around 90% success because some of the logo pieces have a group of white at the top and bottom. This makes it so the bottom piece of a logo and the top piece of the logo make good fits for the middle and bottom rows. Example from my solver: http://imgur.com/CQvcH.png

The photos take up the entire frame with various colors instead of one solid one, so it is not likely for any of them to end up with a mismatch like this.

Oh, that's a really interesting case! I hadn't seen any like that when I posted, but that's definitely something to consider. I think you could work around whenever you get multiple "perfect" fits like that by comparing a) whether they are non-blank, or, more sophisticated, b) are there continuous edges across the boundary.

Broken: http://pastie.org/656332

Naive attack, but it works well in my testing (ran it about 10 times, 100% success rate). If you have PIL installed, just run it through python and it'll grab an image and print whether it succeeded or failed to verify its solution.

Or a Greasemonkey script: http://pastie.org/656481

(Adds a "Solve" link that moves the image rows into a solved position. Tested in Firefox 3.5.)

Slightly off topic: The bag-of-potatoes puzzle could trip some people up.

The stated problem is: “You have a 100 pound bag of potatoes. 99% of the bag is water weight. You leave the bag in the sun for a few hours. Now you bring it in and it is only 98% water weight, due to evaporation. What is the new total weight of the bag of potatoes?”

The first-reaction answer is that the bag now weighs 98 pounds. But originally the bag contained 1 lb of solid, 99 pounds of water. (Let's assume no other liquids than water). After evaporation, you still have 1 lb of solid, but it's now 2% of the total weight. For 1 pound of solid to equal 2% of total weight, the total weight has to be 50 pounds. That means the bag has only 49 pounds of water remaining. (That seems like a lot of evaporation for just a few hours in the sun.)

I don't understand how you reached the conclusion that the 1lb of solid becomes 2% of the total weight after evaporation.

Seems to me that it would be 1.01%.

The statement of the problem says that, after evaporation, the bag is now 98% water by weight, meaning that the solid matter is now 2% (100% - 98%) instead of the 1% it started out as.

Per the problem statement, the 100-pound bag was initially 99% = 99 pounds of water. The non-water part (which we'll assume for simplicity was non-volatile solids) was therefore 100 pounds - 99 pounds = 1 pound. Solids don't evaporate, so even after evaporation, the 1 pound of solid matter remains. That 1 pound is now 2% = 1/50 of the weight, per above. The total weight after evaporation is therefore 50 pounds.

Ah, I see. I'm slow.


- Easier to defeat than OCR.

- Only 9 combinations, so random guessing works fine too.

- Visually impaired fail.

- Utterly dependent on a mouse. This is annoying.

reliance on javascript

I don't think that is a failure though - that alone removes a lot of bots.

Or may be this is the next big thing. ;) http://www.makeuseof.com/tech-fun/break-this-captcha/

Captcha is futile as a way to prevent people spamming, but a great way to push funding for emerging areas in Computer Science. I recommend we go with image edge detection next.

It's safe to say the author has no concept of how sophisticated CAPTCHA breakers are these days. This would last about five minutes on Gmail before being cracked.

Money-motivated "arms races" like this might well be a driver for the evolution of technologies that, collectively, could be called "artificial intelligence." (This thought probably isn't original to me, but I can't think of where I might have read it.)

I doubt solving a puzzle is a good idea for the conversation rate. It would be interesting to see some A/B testing results...

It is much more fun than a captcha.

Heh, the article has been pulled.

The next big thing in turning visitors away.

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