Crossroads The ACM Magazine for Students

Sign In

Association for Computing Machinery

Magazine: Features Profile Luis von Ahn

Profile Luis von Ahn

By ,

Full text also available in the ACM Digital Library as PDF | HTML | Digital Edition

Tags: Document types, Information retrieval, Information storage systems, Learning settings, Web-based interaction

back to top 

In 2002, Luis von Ahn had a crazy idea: he wanted to use an online computer game to perform the tedious task of "image labeling," or identifying pictures and assigning them textual descriptions. The problem with crazy ideas, of course, is that they sound a little crazy, and so it's hard to get other people to believe in them. Von Ahn's first paper about the game was rejected from the ACM Conference on Human Factors in Computing Systems [also known as "CHI"] with some of the lowest reviewing scores possible.

Uninterested in taking "no" for an answer, von Ahn spent several months realizing his idea as a web-based game called the ESP Game. In the ESP Game, a player logs into a web site and is paired up with another random player. The two players both see the same image and are asked to write words that describe it. As soon as the two players write the same word, they win the round, and a new image appears. Behind the scenes, the matched words are then used as labels for the image. In the first four months of its operation, the ESP Game generated more than a million labels for more than a quarter of a million images.

The game is available to anyone to play at Games with a Purpose: http://www.gwap.com.

His paper, now with a very significant proof-of-concept, cruised to acceptance at the 2004 CHI conference with rave reviews.

Experiences like this have made von Ahn accept the fact that it sometimes takes extra work to prove everyone else wrong. Not only do ideas like the ESP Game take months or years to develop, but the development of those ideas requires collaboration across many areas of computer science. When it comes to developing games, it's not enough for the human computation aspects to work correctly. The game has to be fun, easy-to-use, and capable of handling potentially millions of people trying to play simultaneously.

While the ESP Game has certainly come into its own, von Ahn is perhaps better known for creating Captcha, a system that helps distinguish humans from bots online, and its spin-off ReCaptcha.

ReCaptcha works by showing people pictures of words that a computer had trouble recognizing as text and asking people to type it. Ticketmaster likes it because it helps ensure that the company is interacting with a person and not a scalper's computer program. Von Ahn likes it because, by typing in the word that appears in a difficult-to-read image, software that he and his team designed can reliably turn pictures of a book into words. However, not-so-good people in the real world, like scalpers and organized crime syndicates, want access to the resources that ReCaptcha protects, whether free email accounts, concert tickets, or Craigslist postings, and the results are sometimes disturbing. While von Ahn says he's never felt threatened directly, it did hit a little too close to home when people tried to turn off some of ReCaptcha's servers by breaking into a Los Angeles facility where they were stored.

In the first four months of its operation, the ESP Game generated more than a million labels for more than a quarter of a million images.

Von Ahn spends much of his time at Carnegie Mellon University teaching undergraduates and advising graduate students. Teaching, in particular, is a frequent topic on his aptly-named web site "Luis von Blog" [http://vonahn.blogspot.com], another place where he is unafraid of controversy.

One blog post, where von Ahn weighed the advantages of outsourcing graduate students to third-world countries, came with the following disclaimer: "100 percent of my PhD students are working on projects of their own choosing." Even though they have a well-known advisor, von Ahn says that the graduate students he advises have not found it difficult to differentiate their work from his. Most of them identify with different areas of computer science and publish in different conferences.

It helps that von Ahn is uninterested in fitting into a field, whereas many other researchers find it important to concentrate on a particular area of computer science. The CMU professor thinks that's just crazy, even if holding that belief implies, as he says, that "everyone is crazy but me."

back to top  Footnotes

DOI: http://doi.acm.org/10.1145/1869086.1869102

back to top 

©2010 ACM  1528-4972/10/1200  $10.00

Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee.

The Digital Library is published by the Association for Computing Machinery. Copyright © 2010 ACM, Inc.


There are no comments at this time.


To comment you must create or log in with your ACM account.


Flickr group for funny reCaptchas

http://www.flickr.com/groups/[email protected]/pool/

Games With a Purpose




Complete Automated Public Turing test to tell Computers and Humans Apart: A contrived acronym intentionally redolent of the word “capture,” used to describe a test issued on web forms to protect against automated responses.


Game with A Purpose: a term used to describe a computer game that layers a recreational challenge on top of a problem that demands human intelligence for efficient solution, e.g.: protein folding.


Human-Guided Search: A research project investigating a strategy for search and optimization problems that incorporates human intuition and insight.