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Are CAPTCHAs case sensitive?


Many sites, for example Skydrive, try to stop robots entering by requiring
you to enter a string of letters which have distorted shapes. I cannot seem to
get it right. Is case important? I cannot distinguish between lower and
uppercase for the letters.

In this excerpt from
Answercast #93
I look at CAPTCHA tests on website forms that ask you to
prove you are not a robot, and how to pass the test.


CAPTCHAs case sensitive

Unfortunately, the answer to “does case matter” depends on the site and the technology that they happen to be using to perform this little test.

The test by the way is called a CAPTCHA, a “Completely Automated Program to Tell Computers and Humans Apart.”

The idea is that computers, currently, can’t interpret those pictures and humans are supposed to be able to. The reality is that many of those images are excessively distorted and it can be really hard to tell exactly what those letters are.

Passing the CAPTCHA test

Now, the thing to do in a case like that is – most CAPTCHAs (most that I’ve seen these days) actually have two additional options associated with them.

One is they allow you to say, “I can’t understand this one, give me a different one.” So you can actually cycle through a number of different CAPTCHAs, and based on one that you find you can understand, you can type in the correct response.

The other approach is that most of them have an accessibility option for people that can’t see or can’t see well enough. They will sometimes play an audio CAPTCHA where you simply type in what you hear. That may be an alternative if the CAPTCHA is too difficult for you.

It depends…

Unfortunately, like I said, the technologies are different depending on what sites you visit. The one that I happen to use on a couple of my other sites is called RECAPTCHA. It’s based on computer technology developed out at Cornell, if I’m not mistaken. It is actually used to perform very slow, massive, digitization of books.

So you’re presented with two words; one of which the CAPTCHA actually knows and you must get right, the other of which the CAPTCHA… well it actually doesn’t know and it’s asking you to express an opinion on just what those letters are. It then takes multiple answers from multiple different people and sort of averages it out. If everybody agrees on what the word is then the CAPTCHA knows that that word from that book is actually this.

So, there you go. I think that the best thing, in general, to do is to try a different CAPTCHA if they give you the option to refresh and if not, give the accessibility options a try to see if that doesn’t get you passed as well.

(Transcript lightly edited for readability.)

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8 comments on “Are CAPTCHAs case sensitive?”

  1. The other question that crops up from time to time with regards to CAPTCHA’s is “Is a space required between two words”…

    …Of course, that is also an ‘It depends’ answer. I’ve only ever seen one CAPTCHA that actually specified whether the space was required or not.

    It does have me wondering whether the space I’ve used, or lack of one, has caused the ‘failure’, as I thought I had all the letters correct!

  2. The only frustating thing about “prove you are human” techniques is when the technique itself is failing. I’ve been to sites that won’t let me get past the captcha check despite my indefatigable attempts at passing. I’m talking 50 to 60 tries, just to prove to myself that THIS site isn’t functioning properly. It has happened to me 3 times in the last year or so. My guess is that it could be the site or it could be the sites communication to the captcha server but probability says it can’t be me.

  3. At 73 with slowly fading eyesight, I dislike captcha’ with a passion. I’ve often had to try another one 30, 40, 50 times and give up. I cannot distinguish many of the squiggly little symbols Many more enlightened sights use simple math: “what is 2 + 2?” Others show a wiggling tif file. There are many options available without using captcha.

  4. I agree with Bob Price particularly, being older than him

    Expanding on his comments, there are those sites, all too many, that insist on using poorly contrasting font colours against the prevailing background, eg dark grey font on a light grey background.

    And very small font sizes.

    Yes, there are the Disability Options and other ways such as highlighting as for COPYing; but why should we have to go to these lengths, simply to make sites legible.

    Back around 1990, Microsoft commissioned research about such aspects; and I read the report once on the early Web; but have not found it since.

  5. My eyes are failing too, and find many captchas hard to decipher. If I can, I use Ctrl_+ to make the captcha big enough that I can read it (ctrl_0 resets zoom) If I can’t, I use screen capture (in Paintshop Pro) to snag the captcha image and blow it up. That almost always works.

  6. Alex Dow’s comment about poorly contrasting font and background colours is so true, not only in terms of CAPTCHAS but also in website content. I do not understand why some websites persist with ignoring common sense. Aesthetism is rarely a viable excuse. One of the reasons why I have subscribed to Ask Leo, is because it is easy to read.

  7. I use a magnifying glass to ensure I am seeing
    every character elearly, and yet I can type in
    the characters again and again and fail the test.
    There is something wrong with this type of captcha.
    I passed the Graduate Record Exam. Alas! I have
    been locked out of very vital information more than
    once. This cannot always remedied with a phone call.
    I am just locked out and I won’t type Captchas all day.

  8. I’ve tried the audio CAPTCHAs and they were worse than the originals. Since this article was written, most CAPTCHAs use the select all photos containing a certain item. A bit of an improvement for me, but I still hate them. I liked the ones that uses a simple arithmetic problem. I don’t see those anymore. I guess they were too easy for the bots.


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