Abstract:Since about 2003, CAPTCHAs have been widely used as a barrier against bots, while simultaneously annoying great multitudes of users worldwide. As their use grew, techniques to defeat or bypass CAPTCHAs kept improving, while CAPTCHAs themselves evolved as well, becoming increasingly difficult to solve for both bots and…

Abstract: Linear bandits and contextual bandits are online learning problems that have a wide range of applications, including recommendation systems, healthcare and many others. For instance, a search for “linear contextual bandit” on Google Scholar over the past five years yields over 17,000 papers. In contextual bandits, a…