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CAPTCHA is a test to distinguish humans from bots on websites, often involving distorted images or audio. Learn about its origin, purpose, characteristics, and challenges for accessibility and artificial intelligence.
reCAPTCHA is a CAPTCHA system owned by Google that distinguishes between human and automated access to websites. It started as a project to digitize books and images, and now uses behavioral analysis and image recognition to verify users.
MNIST database is a large collection of handwritten digits images used for training and testing image processing and machine learning systems. It is derived from NIST's original datasets and has 60,000 training and 10,000 testing images, as well as an extended version with letters.
Scale invariance is a property of objects or laws that do not change under rescaling of length, energy, or other variables. Learn about scale-invariant functions, curves, distributions, processes, and phenomena in physics, mathematics, statistics, and cosmology.
Luis von Ahn is a Guatemalan entrepreneur and computer scientist, known for inventing CAPTCHA, reCAPTCHA and Duolingo. Learn about his early life, education, career, research and awards on Wikipedia.
An image moment is a weighted average of image pixels' intensities, useful to describe objects after segmentation. Learn about raw, central and Hu moments, their invariants, and how they are used in image analysis and recognition.
A theory of object recognition that breaks down objects into geons, basic 3-dimensional shapes that can be combined in various arrangements. Geons are invariant across viewpoint and enable us to recognize objects from different angles.
In early CAPTCHAs, the challenge sent to the user was a distorted image of some text, and the user responded by transcribing the text. The distortion was designed to make automated optical character recognition (OCR) difficult and prevent a computer program from passing as a human.