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Invariant recognition refers to the ability to recognize letters despite a large amount of variation in their shapes. [25] Segmentation is the ability to separate one letter from another, made difficult in CAPTCHAs. Parsing refers to the ability to understand the CAPTCHA holistically, in order to correctly identify each character. [26]
reCAPTCHA Inc.[1] is a CAPTCHA system owned by Google. It enables web hosts to distinguish between human and automated access to websites. The original version asked users to decipher hard-to-read text or match images. Version 2 also asked users to decipher text or match images if the analysis of cookies and canvas rendering suggested the page ...
The MNIST database (Modified National Institute of Standards and Technology database[1]) is a large database of handwritten digits that is commonly used for training various image processing systems. [2][3] The database is also widely used for training and testing in the field of machine learning. [4][5] It was created by "re-mixing" the ...
t. e. The scale-invariant feature transform (SIFT) is a computer vision algorithm to detect, describe, and match local features in images, invented by David Lowe in 1999. [ 1 ] Applications include object recognition, robotic mapping and navigation, image stitching, 3D modeling, gesture recognition, video tracking, individual identification of ...
Visual object recognition refers to the ability to identify the objects in view based on visual input. One important signature of visual object recognition is "object invariance", or the ability to identify objects across changes in the detailed context in which objects are viewed, including changes in illumination, object pose, and background context.
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.
Software that could reverse CAPTCHA with some accuracy by analysing patterns in the generating engine started being developed soon after the creation of CAPTCHA. [96] In 2013, researchers at Vicarious announced that they had developed a system to solve CAPTCHA challenges from Google , Yahoo! , and PayPal up to 90% of the time. [ 97 ]
Class-invariance. A very common type of prior knowledge in pattern recognition is the invariance of the class (or the output of the classifier) to a transformation of the input pattern. This type of knowledge is referred to as transformation-invariance. The mostly used transformations used in image recognition are: translation; rotation;