WYSIWYG NPR: drawing strokes directly on 3D models
Proceedings of the 29th annual conference on Computer graphics and interactive techniques
ACM Transactions on Graphics (TOG)
Content-Based Ima e Orientation Detection with Support Vector Machines
CBAIVL '01 Proceedings of the IEEE Workshop on Content-based Access of Image and Video Libraries (CBAIVL'01)
Human facial illustrations: Creation and psychophysical evaluation
ACM Transactions on Graphics (TOG)
Telling humans and computers apart automatically
Communications of the ACM - Information cities
IEEE Transactions on Pattern Analysis and Machine Intelligence
Asirra: a CAPTCHA that exploits interest-aligned manual image categorization
Proceedings of the 14th ACM conference on Computer and communications security
Upright orientation of man-made objects
ACM SIGGRAPH 2008 papers
Proceedings of the 9th workshop on Mobile computing systems and applications
What's up CAPTCHA?: a CAPTCHA based on image orientation
Proceedings of the 18th international conference on World wide web
ACM SIGGRAPH Asia 2009 papers
CAPTCHA: using hard AI problems for security
EUROCRYPT'03 Proceedings of the 22nd international conference on Theory and applications of cryptographic techniques
Recognizing objects in adversarial clutter: breaking a visual captcha
CVPR'03 Proceedings of the 2003 IEEE computer society conference on Computer vision and pattern recognition
Collaborative filtering CAPTCHAs
HIP'05 Proceedings of the Second international conference on Human Interactive Proofs
Automatic image orientation detection
IEEE Transactions on Image Processing
Directing gaze in 3D models with stylized focus
EGSR'06 Proceedings of the 17th Eurographics conference on Rendering Techniques
Enhanced STE3D-CAP: a novel 3d CAPTCHA family
ISPEC'12 Proceedings of the 8th international conference on Information Security Practice and Experience
Breaking a 3d-based CAPTCHA scheme
ICISC'11 Proceedings of the 14th international conference on Information Security and Cryptology
A survey and analysis of current CAPTCHA approaches
Journal of Web Engineering
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This paper introduces a captcha based on upright orientation of line drawings rendered from 3D models. The models are selected from a large database, and images are rendered from random viewpoints, affording many different drawings from a single 3D model. The captcha presents the user with a set of images, and the user must choose an upright orientation for each image. This task generally requires understanding of the semantic content of the image, which is believed to be difficult for automatic algorithms. We describe a process called covert filtering whereby the image database can be continually refreshed with drawings that are known to have a high success rate for humans, by inserting randomly into the captcha new images to be evaluated. Our analysis shows that covert filtering can ensure that captchas are likely to be solvable by humans while deterring attackers who wish to learn a portion of the database. We performed several user studies that evaluate how effectively people can solve the captcha. Comparing these results to an attack based on machine learning, we find that humans possess a substantial performance advantage over computers.