CAPTCHA Economics

CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) are the distorted text puzzles that are designed to keep spammers out of websites.  Although some AI systems have been developed to solve CAPTCHAs the market has discovered that it is cheaper to farm out the problems to workers in developing countries.

Here is an amazingly detailed investigation from researchers at UC San Deigo of the market for solving CAPTCHAs.

Bottom line:

  • Prices run about $1 per thousand CAPTCHAs solved, depending on the time of
    day and demand.
  • The median response time to solve a CAPTCHA is 14
    seconds and accuracy runs about 90%.
  • “[T]he
    business of solving CAPTCHAs,…is a well developed, highly-competitive industry with the capacity to solve on the order of a million CAPTCHAs per

Hat tip: Mim’s Bits.


1,000,000 CAPTCHAs per day doesn't seem like that many. 389 people working 10 hour days solving 1 CAPTCHA per 14 seconds can handle this volume. (4.285 per minute * 60 mins * 10 hours = 2571 CAPTCHAs per person per 10 hour day. 1,000,000 / 2571 = 389)

Another account of farming out CAPTCHAs - Google has an ingenious service that uses CAPTCHAs to help fix garbled text when books are scanned for Google books. Basically when books are scanned, some text comes out blurry and distorted and unreadable by computers, but the words are readable by humans. Since computers are doing the scanning, some words get recorded as gibberish. ReCAPTCHA takes those distorted, blurry images unreadable by computers and uses them as CAPTCHAs to obtain the correct word for their database.

More info here -

Computers could do many orders of magnitude more spamming than a human could without CAPTCHAS, so it looks like they're fairly effective in limiting spamming.

No, Manto, the $2.60 is about correct. Buried within the paper, the top 100 earners at one of the CAPTCHA services averaged $47 per month. That is about what a textile factory worker makes in the Far East, and the authors of the paper conclude that they compete for the same labor pool.

*UC San Diego.

14 seconds is the average? I hate to say it but sometimes you really can't tell if it's an upper case or lower case letter. I'm shocked the average isn't closer to 30 seconds.

Defenders have gone a bit further - instead of trying to make a person prove they are human, they make a person prove they are a specific human.

In order to get back onto my Facebook account today (my password was compromised, perhaps by a very clever phishing attack - I usually spot those a mile away) I had to go through a process of looking at pictures of my friends, and identifying which friends they I have over a thousand people on my friends list, it is clear they managed to pick the ones I know best, because I managed.

To post on this thread, you must prove that P != NP

You could also think up other, more elaborate ways to discriminate between specific demographics.

Blog readers liable to post worthwhile comments have many years of experience extensively reading English sentences daily, so you could tailor a challenge for this. For icsnatne, tpye tihs sbrmcaeld snetncee wtih cerocrt slepnlig. It is a surprising empirical observation that as long as the first and last letters of each word remain fixed, most of us can decipher such sentences without much difficulty.

Or, provide an extremely low-fidelity distorted and staticky sound clip of a short whispered phrase and ask people to type it in: this filters out non-native speakers, since listening comprehension is one of the trickier aspects of learning a foreign language. It also filters out people who can't spell (pick moderately difficult words like "hierarchy"). With ultra-low fidelity, the bandwidth should be comparable to presenting a GIF image.

Requiring a micropayment to post a message might effectively filter spam. Even one cent per message (giving a whole new meaning to the phrase "a penny for your thoughts") would raise spammers' costs by a factor of ten.

While micropayments are notoriously vaporware on the broader web, they are entirely possible on walled-garden platforms that provide their own virtual currency credits or payment systems (eg, Facebook, soon).

Who knows, you could even use the pennies generated to pay some textile-factory guy to manually clean up the spam postings that get through...

Instead of treating every posted comment exactly the same, why not do a little discriminatory profiling?

Spam postings inevitably include outbound links in the body of the message. Often several, in fact. For every outbound link detected in the message body, triple the length of the CAPTCHA.

The goal is not to make the challenge impossible, but simply to balloon the spammers' costs.

Do MR readers really want to have to deal with listening to quiet whispers everytime they post? Proabably not. The turing test has to be hard enough for a computer not to easily decipher, and easy enough that you dont' turn away people you actually want.

If you are a legitimate MR poster bestowing your priceless insights upon an awestruck and grateful world, the time spent solving a slightly more elaborate challenge is an infinitesimal fraction of the time you spent thoughtfully drafting and editing your pearls of wisdom. It's not a bug, it's a feature!

'I know some folks know how to live cheaply on this planet, but not this cheaply. One or more of the figures Alex has presented must be wrong.'

Actually, I believe some people actually do.

Whenever CAPTCHAs were discussed on Slashdot the workaround people always came up with wasn't paying people in cash. It was to start a porn site that required you to solve a CAPTCHA to view the content, and for your CAPTCHA, just show the CAPTCHA you need solved. If you have high traffic, this could work without having to wait long for a horny visitor to provide you with the answer.

But I'm guessing the article found people third worlders actually professionally solving CAPTCHAs.

Just now the FFXIV Gil at yesterday, because my friends scolded by hw mother, he mother said that spend more time to play only want to get more FFXIV Gold, then forget the study, and also need money to buy FF14 Gil, his mother can not get he money, so he was very sad, he want to borrow money to me and go on to buy FF14 gold, I was very atonement, I only hope he can bought the Final Fantasy XIV Gil.

I had seen some captcha companies offering as little as 60 cents per thousand captchas. I am not sure if someone had bitten it. The one dollar per thousand Is low for someone who is making both ends meet even in a third world country.

Don and Luca Masters, I call BS on porn for captchas. boingboing says "Someone told me about [it]" without providing a link or any other evidence. The BBC's confused story (is it a windows based game or a browser hijack?) doesn't give any evidence either. Why can't I find this program on the net for download? Urban legend until proven otherwise.

Bob Knaus, $2.60/day isn't even enough to pay internet cafe fees! Not in the urban centres (of countries like China, Vietnam, India, and Thailand), where internet access is cheapest, and definitely not in rural areas. I suppose it's possible that these captcha companies are providing computers and feeding and housing their workers, but that would mean the actual wage the workers are getting is higher than the reported figure and the cost to the companies is higher still.

And $47/month as the going wage is from a time long past. These days, low-paid factory workers earn more like $140/month.

@Manto: I have personal knowledge of this practice because, at a previous job, I became aware of it while working with a team developing a Captcha. Unfortunately for me to give you enough information to authenticate this I'd have to identify the employer and the project which I'm not at liberty to do, and so that makes my response unverifiable. I wouldn't trust a guy who says "trust me" on the Internet either...

WTC because of any Islamic influences to its architecture.

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