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>Moving the slider bit by bit and OCRing will solve 90% of the images I've seen. I'm not sure what you're saying. Good OCR should recognize the text when it's

by jere 14y ago

>Moving the slider bit by bit and OCRing will solve 90% of the images I've seen. I'm not sure what you're saying. Good OCR should recognize the text when it's distorted slightly, right? Which would yield false positives, no? As much as I'd like to pick this apart, I think the slide captcha is actually pretty clever. We can nitpick implementation details all day, but most of those can be fixed. I wish I had thought of it.

mikle 14y ago
To be honest the only reason I didn't add "yet another misguided captcha attempt" to the title is because of the advertising aspect. We can and should nitpick captchas, even just if it is as an intellectual exercise. About the OCR - what I meant is that most of their images had text meaning I can OCR every step and if I get something with dictionary words I submit. It will work even the OCR is very permissive (recognizes distorted text as you put it) because this implementation accepts not only the perfect straight solution but also "close enough"s.
- jere 14y ago
  >About the OCR - what I meant is that most of their images had text meaning I can OCR every step and if I get something with dictionary words I submit. It will work even the OCR is very permissive (recognizes distorted text as you put it) because this implementation accepts not only the perfect straight solution but also "close enough"s. Again, fair point on this particular implementation. However, there's no reason to have the fudge factor. It's already plenty easy to get the exact answer. Ignoring that fudge factor, there are at least 6 options on each side of the correct answer that (I would assume) can be OCRed also. So the OCR method only cuts out maybe half of the wrong answers... perhaps better because the correct one will me closer to the middle? I think a more foolproof attack vector would be too look for vertical and horizontal lines, which are only going to show up in the correct image.
  - mikle 14y ago
    I'm not sure it will be more foolproof since images don't really need to have long horizontal or vertical lines, but it is indeed another great attack path.
    - jere 14y ago
      If it has non-handwritten text, it will. If it has a banner or button, it will. If the layout contains a rectangle or divider or border, it will. I don't expect to see ads without the previously mentioned items very often.

by jere 14y ago

mikle 14y ago

To be honest the only reason I didn't add "yet another misguided captcha attempt" to the title is because of the advertising aspect. We can and should nitpick captchas, even just if it is as an intellectual exercise. About the OCR - what I meant is that most of their images had text meaning I can OCR every step and if I get something with dictionary words I submit. It will work even the OCR is very permissive (recognizes distorted text as you put it) because this implementation accepts not only the perfect straight solution but also "close enough"s.

jere 14y ago
>About the OCR - what I meant is that most of their images had text meaning I can OCR every step and if I get something with dictionary words I submit. It will work even the OCR is very permissive (recognizes distorted text as you put it) because this implementation accepts not only the perfect straight solution but also "close enough"s. Again, fair point on this particular implementation. However, there's no reason to have the fudge factor. It's already plenty easy to get the exact answer. Ignoring that fudge factor, there are at least 6 options on each side of the correct answer that (I would assume) can be OCRed also. So the OCR method only cuts out maybe half of the wrong answers... perhaps better because the correct one will me closer to the middle? I think a more foolproof attack vector would be too look for vertical and horizontal lines, which are only going to show up in the correct image.
- mikle 14y ago
  I'm not sure it will be more foolproof since images don't really need to have long horizontal or vertical lines, but it is indeed another great attack path.
  - jere 14y ago
    If it has non-handwritten text, it will. If it has a banner or button, it will. If the layout contains a rectangle or divider or border, it will. I don't expect to see ads without the previously mentioned items very often.