CAPTCHA - Revision history

Dangelsm at 07:33, 9 April 2009

2009-04-09T07:33:27Z

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	An interesting feature of reCAPTCHA is that the human-provided solutions are used to digitize old texts. Each word displayed in the CAPTCHA is taken from a scanned text. One of the words was not recognizable by optical character recognition (OCR), while the other was. The user is then asked to enter both words. The word that was recognized by OCR is used to grade the CAPTCHA, while the user's solution to the unrecognized word is used, together with other user's solutions of the same image, to digitize the text. reCAPTCHA is currently helping to digitize old books from the Internet Archive and old editions of the New York Times [1].		An interesting feature of reCAPTCHA is that the human-provided solutions are used to digitize old texts. Each word displayed in the CAPTCHA is taken from a scanned text. One of the words was not recognizable by optical character recognition (OCR), while the other was. The user is then asked to enter both words. The word that was recognized by OCR is used to grade the CAPTCHA, while the user's solution to the unrecognized word is used, together with other user's solutions of the same image, to digitize the text. reCAPTCHA is currently helping to digitize old books from the Internet Archive and old editions of the New York Times [1].
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		+	<div style="clear:both;"></div>

	==References==		==References==

Dangelsm: /* See Also */

2009-04-09T07:32:00Z

Dangelsm at 07:26, 9 April 2009

2009-04-09T07:26:42Z

← Older revision		Revision as of 07:26, 9 April 2009
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	# W3C. 2005. [http://www.w3.org/TR/turingtest/ Inaccessibility of CAPTCHA].		# W3C. 2005. [http://www.w3.org/TR/turingtest/ Inaccessibility of CAPTCHA].
	# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].		# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].
		+
		+	==See Also==
		+	[[Electronic Voting Systems]]
		+
		+	[[Cryptography in Information Security]]

	==External Links==		==External Links==

Dangelsm at 07:21, 9 April 2009

2009-04-09T07:21:10Z

← Older revision		Revision as of 07:21, 9 April 2009
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	==Weaknesses==		==Weaknesses==
-	[[Image:Sin_captcha.jpg\|thumb\|A particularly poor CAPTCHA. This test is too difficult for the average user to solve in a reasonable about of time.]]	+	[[Image:Sin_captcha.jpg\|thumb\|A particularly poor CAPTCHA. This test is too difficult for the average user to solve in a reasonable about of time. [5]]]
-	[[Image:Aicaptcha.jpg\|thumb\|A CAPTCHA that has been successfully solved by a computer]]	+	[[Image:Aicaptcha.jpg\|thumb\|A CAPTCHA that has been successfully solved by a computer [2]]]

	===Poorly Made CAPTCHA===		===Poorly Made CAPTCHA===
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	Although it can be said that these are examples of ''poor'' CAPTCHA, based on the very definition of a CAPTCHA these are not CAPTCHA at all. If a test is either not solvable by humans or solvable by computers, it is not longer a test that tells computers and humans apart		Although it can be said that these are examples of ''poor'' CAPTCHA, based on the very definition of a CAPTCHA these are not CAPTCHA at all. If a test is either not solvable by humans or solvable by computers, it is not longer a test that tells computers and humans apart

-	[[Image:Unreadable_captcha.jpg\|thumb\|left\|Another poor CAPTCHA. The text in this image is unreadable by a human.]]	+	[[Image:Unreadable_captcha.jpg\|thumb\|left\|Another poor CAPTCHA. The text in this image is unreadable by a human. [5]]]

	===Accessibility===		===Accessibility===
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	==Implementation==		==Implementation==

-	[[Image:Recaptcha-example.gif‎\|thumb\|300px\|An example of reCAPTCHA, the currently recommended CAPTCHA implementation]]	+	[[Image:Recaptcha-example.gif‎\|thumb\|300px\|An example of reCAPTCHA, the currently recommended CAPTCHA implementation [1]]]

	The currently recommended CAPTCHA implementation is reCAPTCHA, developed by Carnegie Mellon University. It includes both a standard bitmap text CAPTCHA as well as an audio CAPTCHA for accessibility. As of present, the image distortion techniques used by reCAPTCHA are not computer solvable.		The currently recommended CAPTCHA implementation is reCAPTCHA, developed by Carnegie Mellon University. It includes both a standard bitmap text CAPTCHA as well as an audio CAPTCHA for accessibility. As of present, the image distortion techniques used by reCAPTCHA are not computer solvable.

Dangelsm at 07:20, 9 April 2009

2009-04-09T07:20:04Z

← Older revision		Revision as of 07:20, 9 April 2009
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	==Background==		==Background==

-	The term CAPTCHA was first coined by Luis von Ahn, Manuel Blum, Nicholas J. Hopper and John Langford in 2000. von Ahn, Blum and Hopper were all from Carnegie Mellon University, while Langford was from IBM. In their paper "CAPTCHA: Using Hard AI Problems for Security" [4], they introduced the theoretical concept of CAPTCHA and some examples of how they could be used. They described a CAPTCHA as "a cryptographic protocol whose underlying hardness assumption is based on an AI problem" [4]. This can be compared to standard key-based cryptography where the "underlying hardness assumption" is that factoring of large numbers is hard. Further, they concluded that a CAPTCHA is a win-win situation, as either the CAPTCHA remains unsolvable by computers and security is maintained, or it is cracked by a computer program and the field of artificial intelligence has been advanced.	+	The term CAPTCHA was first coined by Luis von Ahn, Manuel Blum, Nicholas J. Hopper and John Langford in 2000. von Ahn, Blum and Hopper were all from Carnegie Mellon University, while Langford was from IBM. In their paper "CAPTCHA: Using Hard AI Problems for Security" [3], they introduced the theoretical concept of CAPTCHA and some examples of how they could be used. They described a CAPTCHA as "a cryptographic protocol whose underlying hardness assumption is based on an AI problem" [3]. This can be compared to standard key-based cryptography where the "underlying hardness assumption" is that factoring of large numbers is hard. Further, they concluded that a CAPTCHA is a win-win situation, as either the CAPTCHA remains unsolvable by computers and security is maintained, or it is cracked by a computer program and the field of artificial intelligence has been advanced.

	==Applications==		==Applications==
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	===Accessibility===		===Accessibility===

-	Many CAPTCHA also suffer from poor accessibility. For example, each of the CAPTCHA shown here would be unusable by a blind user as they require the user to decipher text from a bitmap image. Text-only CAPTCHA are also equally inaccessible to users suffering from disabilities such as dyslexia. Some websites now provide an audio CAPTCHA as well, though these are sometimes equally difficult to understand by humans, or easier to crack with speech-recognition software [6]. As such, the W3C has recommended that low-volume, low-resource websites (such as blogs protecting against comment spam) replace CAPTCHA with spam-filtering heuristics [6].	+	Many CAPTCHA also suffer from poor accessibility. For example, each of the CAPTCHA shown here would be unusable by a blind user as they require the user to decipher text from a bitmap image. Text-only CAPTCHA are also equally inaccessible to users suffering from disabilities such as dyslexia. Some websites now provide an audio CAPTCHA as well, though these are sometimes equally difficult to understand by humans, or easier to crack with speech-recognition software [4]. As such, the W3C has recommended that low-volume, low-resource websites (such as blogs protecting against comment spam) replace CAPTCHA with spam-filtering heuristics [4].

	<div style="clear:both;"></div>		<div style="clear:both;"></div>
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	# Carnegie Mellon University. 2009. [http://recaptcha.net/captcha.html What is a CAPTCHA?].		# Carnegie Mellon University. 2009. [http://recaptcha.net/captcha.html What is a CAPTCHA?].
	# Chesnut, Casey. 2005. [http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]		# Chesnut, Casey. 2005. [http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]
-	# Luis von Ahn, Ben Maurer, Colin McMillen, David Abraham and Manuel Blum. 2008. [http://www.cs.cmu.edu/~biglou/reCAPTCHA_Science.pdf reCAPTCHA: Human-Based Character Recognition via Web Security Measures]. In ''Science''.
	# Luis von Ahn, Manuel Blum, Nicholas Hopper, and John Langford. [http://www.captcha.net/captcha_crypt.pdf CAPTCHA: Using Hard AI Problems for Security]. In ''Eurocrypt''.		# Luis von Ahn, Manuel Blum, Nicholas Hopper, and John Langford. [http://www.captcha.net/captcha_crypt.pdf CAPTCHA: Using Hard AI Problems for Security]. In ''Eurocrypt''.
-	~~# Luis von Ahn, Manuel Blum and John Langford. 2004. [http://www.captcha.net/captcha_cacm.pdf Telling Humans and Computers Apart Automatically]. In ''Communications of the ACM''.~~
	# W3C. 2005. [http://www.w3.org/TR/turingtest/ Inaccessibility of CAPTCHA].		# W3C. 2005. [http://www.w3.org/TR/turingtest/ Inaccessibility of CAPTCHA].
	# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].		# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].
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	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]		[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

-	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)	+	[http://www.cs.cmu.edu/~biglou/reCAPTCHA_Science.pdf reCAPTCHA: Human-Based Character Recognition via Web Security Measures]
		+
		+	[http://www.captcha.net/captcha_cacm.pdf Telling Humans and Computers Apart Automatically]
		+
		+	--[[User:Dangelsm\|Dangelsm]] 03:20, 9 April 2009 (EDT)

Dangelsm: /* External Links */

2009-04-09T07:17:10Z

External Links

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	==External Links==		==External Links==
	[http://en.wikipedia.org/wiki/Captcha CAPTCHA]		[http://en.wikipedia.org/wiki/Captcha CAPTCHA]
-
-	~~[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]~~

	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]		[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)		--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)

Dangelsm: /* External Links */

2009-04-09T07:16:08Z

External Links

← Older revision		Revision as of 07:16, 9 April 2009
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	==External Links==		==External Links==
-	~~[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]~~
-
	[http://en.wikipedia.org/wiki/Captcha CAPTCHA]		[http://en.wikipedia.org/wiki/Captcha CAPTCHA]
		+
		+	[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]

	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]		[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)		--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)

Dangelsm: /* External Links */

2009-04-09T07:15:39Z

External Links

← Older revision		Revision as of 07:15, 9 April 2009
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	==External Links==		==External Links==
-	# [http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]	+	[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]
-	# [http://en.wikipedia.org/wiki/Captcha CAPTCHA]	+
-	# [http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]	+	[http://en.wikipedia.org/wiki/Captcha CAPTCHA]
		+
		+	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)		--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)

Dangelsm: /* External Links */

2009-04-09T07:15:26Z

External Links

← Older revision		Revision as of 07:15, 9 April 2009
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	==External Links==		==External Links==
-	[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]	+	# [http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]
-	[http://en.wikipedia.org/wiki/Captcha CAPTCHA]	+	# [http://en.wikipedia.org/wiki/Captcha CAPTCHA]
-	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]	+	# [http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)		--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)

Dangelsm at 07:15, 9 April 2009

2009-04-09T07:15:12Z

← Older revision		Revision as of 07:15, 9 April 2009
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	# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].		# Willis, John M. 2008. [http://www.johnmwillis.com/other/top-10-worst-captchas/ Top 10 Worst Captchas].

		+	==External Links==
		+	[http://www.brains-n-brawn.com/default.aspx?vDir=aicaptcha Using AI to beat CAPTCHA and post comment spam]
		+	[http://en.wikipedia.org/wiki/Captcha CAPTCHA]
		+	[http://recaptcha.net/learnmore.html Digitizing Books One Word at a Time]

	--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)		--[[User:Dangelsm\|Dangelsm]] 03:12, 9 April 2009 (EDT)

← Older revision		Revision as of 07:32, 9 April 2009
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	[[Cryptography in Information Security]]		[[Cryptography in Information Security]]
		+
		+	[[Digital Signatures]]

	==External Links==		==External Links==