1. A computer-implemented method, comprising: under control of one or more computing devices including executable instructions, acquiring first image information using at least one camera of a computing device; storing, for at least a minimum period of time, the first image information in a rolling buffer; acquiring second image information using the at least one camera; detecting, based at least in part on the second image information, one or more fingers of a user within a specified distance of the computing device; determining, using the second image information, movement of the one or more fingers, the movement corresponding to a first portion of a candidate hand gesture; analyzing the first image information stored in the rolling buffer to detect a second portion of the candidate hand gesture, the second portion having been performed before the first portion of the candidate hand gesture; based at least in part on the first portion of the candidate hand gesture and the second portion of the candidate hand gesture, determining a hand gesture performed by the user; comparing the performed hand gesture to a gesture pattern stored on the computing device; and authenticating an identity of the user as an authorized user, and providing an input to unlock the computing device from a locked state, in response to the hand gesture, performed by the user, being determined to correspond to the gesture stored on the computing device.