RIT news article on Video CAPTCHAs

Posted by Kurt on November 6th, 2009

The RIT Athenaeum has just published a short article describing Video CAPTCHAs. You can find it in print around the RIT campus and online here: http://www.rit.edu/news/story.php?id=47112

Balancing Usability and Security in a Video CAPTCHA

Posted by Kurt on July 13th, 2009

This week (July 15th - July 17th), Richard Zanibbi and I are attending SOUPS ‘09 in Mountain View, CA. It’s a smaller conference that’s gotten great reviews and has had some excellent CAPTCHA-related work presented in the past. On Friday morning, I’ll be presenting a paper titled Balancing Usability and Security in a Video CAPTCHA. A reporter from ZDNet.co.uk has already written a short article about it which you can find here.


The paper can be downloaded here and the slides can be downloaded here. It’s also available at the ACM Digital Library.

Bibtex Entry

	Title = {Balancing Usability and Security in a Video CAPTCHA},
	Author = {Kurt Alfred Kluever and Richard Zanibbi},
	Booktitle = {Proceedings of the 5th Symposium On Usable Privacy and Security 2009},
	Address = {Mountain View, CA, USA},
	Month = {July},
	Year = {2009}

CS Department’s “5 Minutes with Kurt”

Posted by Kurt on March 8th, 2009

You knew you were headed for a career in Computer Science when…
I witnessed the thrill and the excitement of the dot com boom in the late 90’s.

What is your favorite class and why?
Theory of Computer Algorithms. This course is the first formal, in-depth course on algorithms, complexity, and data structures. These three components are the foundations of Computer Science and I highly recommend that everyone take this course (although it is a very difficult course).

One piece of advice I have for 1st year students is…
Establish a relationship with your professors by asking questions in class and utilizing office hours when you are confused.

If you could have dinner with a famous computer scientist, living or dead, who would you choose?
Luis von Ahn. His work on CAPTCHAs and human computation has inspired me to pursue it as my thesis topic.

What is the most interesting project you have worked on, either in a course or on the job?
The most interesting project I’ve worked on has been my thesis. Reading all of the existing research has helped me develop a brand new idea that nobody else in the world has worked on.

Where do you see yourself in ten years?
Hopefully back in school earning my PhD in Computer Science.

Original post: http://www.cs.rit.edu/about/profiles/Kurt_Kluever
PDF version: http://www.cs.rit.edu/five_minutes/pdf/Kurt_Kluever.pdf

Also check out 5 Minutes with Richard Zanibbi (my thesis advisor) and 5 Minutes with Brian Renzenbrink (a good friend).

Video CAPTCHAs at Center for Imaging Science

Posted by Kurt on January 30th, 2009

On January 28th, 2009, my thesis advisor (Richard Zanibbi) presented a talk on Video CAPTCHAs at the RIT Center for Imaging Science. An abstract of the talk can be download here. A video of his talk (with slides) can be watched here using Adobe Acrobat Connect.

MS Thesis available in RIT Library and DML

Posted by Kurt on January 25th, 2009

My thesis is now available in a bounded hard-copy at the RIT library on the 3rd floor (Call No. Q341 .K58 2008) and online through the RIT Digital Media Library.

Video CAPTCHAs: Usability vs. Security

Posted by Kurt on September 13th, 2008

On September 26th, 2008 I will be presenting some of my work on Video CAPTCHAs at the IEEE Western New York Image Processing Workshop 2008 in Rochester, NY. The workshop will be held in the Imaging Science building at RIT (registration details can be found at the above link). The paper is in the form of a 4 page “extended abstract” and can be downloaded below.


The paper can be downloaded here or from the RIT Digital Media Library.

Bibtex Entry

	Title = {Video CAPTCHAs: Usability vs. Security},
	Author = {Kurt Alfred Kluever and Richard Zanibbi},
	Booktitle = {Proceedings of the IEEE Western New York Image Processing Workshop 2008},
	Address = {Rochester, NY, USA},
	Month = {September},
	Year = {2008}

Video CAPTCHA Demo

Posted by Kurt on August 22nd, 2008

If you haven’t already, check out the Video CAPTCHA demo at:


There’s no entrance survey, exit survey and you can quit at any time (don’t feel obligated to finish all 22 videos).  Enjoy!

Evaluating the Usability and Security of a Video CAPTCHA

Posted by Kurt on August 18th, 2008

I just scheduled the time and location for my thesis defense. Everyone is welcome to come, watch, and try to stump me with questions. Hope to see you there! -Kurt

Thesis Statement

One can increase usability while maintaining security in a video CAPTCHA by intelligently extending the set of user-supplied and ground truth tags.


A CAPTCHA is a variation of the Turing test, in which a challenge is used to distinguish humans from computers (”bots”) on the internet. They are commonly used to prevent the abuse of online services. CAPTCHAs discriminate using hard artificial intelligence problems: the most common type requires a user to transcribe distorted characters displayed within a noisy image. Unfortunately, many users find them frustrating and break rates as high as 60% have been reported (for Microsoft’s Hotmail).

We present a new CAPTCHA in which users provide three words (”tags”) that describe a video. A challenge is passed if a user’s tag belongs to a set of automatically generated ground-truth tags. In an experiment, we were able to increase human pass rates for our video CAPTCHAs from 69.7% to 90.2% (184 participants over 20 videos). Under the same conditions, the pass rate for an attack submitting the three most frequent tags (estimated over 86,368 videos) remained nearly constant (5% over the 20 videos, roughly 12.9% over a separate sample of 5146 videos). Challenge videos were taken from YouTube.com. For each video, 90 tags were added from related videos to the ground-truth set; security was maintained by pruning all tags with a frequency ≥ 0.6%. Tag stemming and approximate matching were also used to increase human pass rates. Only 20.1% of participants preferred text-based CAPTCHAs, while 58.2% preferred our video-based alternative.

Finally, we demonstrate how our technique for extending the ground truth tags allows for different usability/security trade-offs, and discuss how it can be applied to other types of CAPTCHAs.

Thesis Committee

Thesis Defense

Time: Thursday, August 28, 2008 at 10:00 a.m.
Location: Building 70, Room 3000


Live Demo


Bibtex Entry

	Title = {Evaluating the Usability and Security of a Video CAPTCHA},
	Author = {Kurt Alfred Kluever},
	School = {Rochester Institute of Technology},
	Address = {Rochester, NY, USA},
	Month = {August},
	Year = {2008}

Video CAPTCHA Experiment

Posted by Kurt on August 7th, 2008

You are invited to try a new video-based CAPTCHA developed within the Computer Science Department at RIT. A CAPTCHA is a challenge designed to distinguish humans from computer programs (’bots’) on the internet; they are typically implemented as a string of distorted characters which must be transcribed.

Many people find the text-based CAPTCHAs frustrating, so we have developed a video-based alternative. In our Video CAPTCHAs, a user must quickly label a video with three tags (words) describing its content.

We would appreciate it if you could help us evaluate the usability of this new approach by completing 20 Video CAPTCHAs. The experiment will only take about 15 minutes of your time. The task may be found at:


Thank you very much for your time.

Kurt Alfred Kluever (MS Student)
Richard Zanibbi (Supervisor)

Document and Pattern Recognition Lab
Department of Computer Science
Rochester Institute of Technology

Video Tagging Experiment

Posted by Kurt on July 1st, 2008


As many of you know, I am in the process of completing my MS thesis in Computer Science at RIT. My area of research is online human verification (i.e., proving that a human is behind an online request, and not an automated computer program). When completing an online form, users are often presented with a distorted string of text which they are forced to transcribe. These are known as CAPTCHAs, and exist to prevent automated programs from abusing online services (humans can read the distorted text but most computer programs cannot). My thesis idea is to create a Video CAPTCHA, where instead of transcribing a string of distorted text, users must supply an appropriate label for a short video (a challenge which computers cannot complete but humans should be able to).

What you can do for me:

I have setup an online data collection website, which will allow me analyze how people label (tag) online videos. You will be asked to quickly tag 20 short online videos. I would greatly appreciate your help in completing the short (10-15 minutes) experiment at the following link:


Feel free to forward this request to anyone else you know who may be interested in participating. If you have any questions, please let me know. The experiment will remain open until July 14th, 2008.

Modified version of Webby Blue
Copyright © 2008 kloover.com. All rights reserved.
**This is my personal blog. The views expressed on these pages are mine alone and not those of my employer.**