Human Computation CSC4170 Web Intelligence and Social Computing Tutorial 7 Tutor: Tom Chao Zhou

Outline Definition & Early Work Human Computation:  Case Study: reCAPTCHA Game with a purpose:  Case Study: ESP Game Q&A Reference

Definition & Early Work Human-based Computation:  Human-based Computation is a computer science technique in which a computational process performs its function by outsourcing certain steps to humans.  This approach leverages differences in abilities and alternative costs between humans and computer agents to achieve symbiotic human-computer interaction.

Definition & Early Work Early Work:  Interactive evolutionary computation.  The idea is proposed by Richard Dawkins (  The preference of a human experimenter is used to guide the evolution of two-dimensional sets of line segments.  This program asks a human to be the fitness function of an evolutionary algorithm, so that the algorithm can use human visual perception and aesthetic judgment to do something that a normal evolutionary algorithm cannot do.

Human Computation Case Study: reCAPTCHA What is CAPTCHA?  A CAPTCHA (completely automated public Turing test to tell computers and humans apart) is a program that can tell whether its user is a human or a computer.  Colorful images with distorted text at the bottom of Web registration forms What is CAPTCHA?  A CAPTCHA (completely automated public Turing test to tell computers and humans apart) is a program that can tell whether its user is a human or a computer.  Colorful images with distorted text at the bottom of Web registration forms

Human Computation Case Study: reCAPTCHA What is CAPTCHA?  It was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University.  Applications of CAPTCHA: Preventing Comment Spam in Blogs. Protecting Website Registration. Online Polls. Preventing Dictionary Attacks. CAPTCHAs can also be used to prevent dictionary attacks in password systems. Search Engine Bots. Preventing search engine bots to crawl the pages.

Human Computation Case Study: reCAPTCHA Statistics about CAPTCHA and some thought.  About 200 million CAPTCHAs are solved by humans around the world every day.  In each case, roughly ten seconds of human time are being spent.  Individually, that's not a lot of time, but in aggregate these little puzzles consume more than 150,000 hours of work each day.  What if we could make positive use of this human effort?

Human Computation Case Study: reCAPTCHA What is reCAPTCHA?  reCAPTCHA does exactly that by channeling the effort spent solving CAPTCHAs online into "reading" books.  reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows.

Human Computation Case Study: reCAPTCHA What is reCAPTCHA?  The old books are being photographically scanned, and then transformed into text using "Optical Character Recognition" (OCR).  However, OCR produces images, which cannot be searched.  reCAPTCHA improves the process of digitizing books by sending words that cannot be read by computers to the Web in the form of CAPTCHAs for humans to decipher.

Human Computation Case Study: reCAPTCHA Ideas of reCAPTCHA:  Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known.  The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one.  The system then gives the new image to a number of other people to determine, with higher confidence, whether the original answer was correct.

Human Computation Case Study: reCAPTCHA Performances of reCAPTCHA:  reCAPTCHA is able to achieve over 99.5% transcription accuracy at the word level.

Game with a purpose (GWAP) Case Study: ESP Game GWAP:  A game with a purpose (GWAP) is a game played on a computer that serves some purpose for the people setting up the game by harnessing human abilities in an entertaining setting.  There are many activities that are almost trivial for humans to perform that have stymied computers, e.g., labelling image.

Game with a purpose (GWAP) Case Study: ESP Game ESP Game:  An effort in human computation originally conceived by Luis Von Ahn of CMU to label images.  Two players attempt to assign the same labels to an image.  The game records the results of matches as image labels and the players enjoy the encounter because of the competitive and timed nature of it.  To ensure that people do their best to accurately label the images, the game requires two people who have only the image in common, to choose the same word as an image label.

Game with a purpose (GWAP) Case Study: ESP Game ESP Game:

Game with a purpose (GWAP) Case Study: ESP Game ESP Game:  Demo:   Play as a guest.

Questions?

Reference reCAPTCHA:     ESP Game:  Homepage of Luis Von Ahn 