| Summary: | 碩士 === 臺中技術學院 === 多媒體設計系碩士班 === 99 === CAPTCHAs (Completely Automated Public Test to tell Computers and Humans Apart) are computer-generated tests designed to differentiate humans from automated programs. The developments of CAPTCHAs are focusing on issues such as the protection of internet resource from being abused by bots. Traditionally, most CAPTCHAs are text-based. But currently, the security of text-based CAPTCHAs encounters a hard challenge from the improvements in OCR (Optical Character Recognition) technology. Therefore, in recent years, various different types of CAPTCHAs are developed with different approaches such as like image-based or audio-based CAPTCHAs.
This paper proposed an image-based CAPTCHA named Puzzle CAPTCHA. Puzzle CAPTCHA utilized image segment technology. In this approach, an image will be embedded with several tetragon cutout blocks with different sizes. The puzzle is built by rotating these original tetragon cutouts by 0, 90, 180, or 270 degrees randomly. Finally, the establishment of Puzzle CAPTCHA is finished by randomly adding interfering lines on the image.
When users face the image of Puzzle CAPTCHA, they click mouse on each tetragon block to make a 90° clockwise rotation of the block. Users should put all tetragon blocks to the right angle to reveal the original image to pass the CAPTCHA test. The preliminary user’s test of Puzzle CAPTCHA shows an 80.4% accuracy rate. Most users can solve the puzzle in less than 10 seconds. Furthermore, the location of tetragon blocks cannot be resolved by current edge detection technology. This could also boost the safety of Puzzle CAPTCHA. The other merit of Puzzle CAPTCHA lies on the universality that it can be implemented without the consideration of language and culture.
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