What's up CAPTCHA?: a CAPTCHA based on image orientation.

Rich Gossweiler Maryam Kamvar Shumeet Baluja

Published in: WWW (2009)

Keyphrases

image retrieval
image data
image features
input image
image content
single image
image analysis
spatial frequency
image representation
image segmentation
high resolution
location and orientation
template matching
image matching
image classification
multiscale
image database
test images
low level
image pixels
position and orientation
image filtering
feature points
image regions
spatial information
gabor filters
object recognition