μcaptcha: Human Interaction Proofs Tailored to Touch-Capable Devices via Math Handwriting
Luis A. Leiva, Francisco Álvaro · International Journal of Human-Computer Interaction · 2015
Online services are often protected with captchas that typically must be solved by typing on a keyboard. Now that smartphones and tablets are increasingly being used to browse the web, new captchas best suited to touch-capable devices should be devised, because entering text on soft keyboards is usually uncomfortable and error-prone. This article contributes to solving this issue with μcaptcha, a novel captcha scheme to tell humans and computers apart by means of math handwriting input. Instead of entering text with a keyboard, the user retypes a mathematical expression on a touch screen using, for example, the finger, a stylus, or an e-pen. Further, as a by-product of solving μcaptcha challenges, a valuable labeled data set of online handwritten math expressions is collected. Studies reveal that μcaptcha is accurate, fast, and easy to perform and that users find it to be both useful and enjoyable. Ultimately, this work informs an understanding of designing better web security measures.