2. A method, comprising: establishing in a processor of a mobile device an imaging field of view for an imager in communication with said processor; defining an input region in said processor within said imaging field of view, said input region being smaller than and substantially fully within said field of view; defining an input in said processor comprising at least one of a hand posture and a hand gesture; defining in said processor an unlock command adapted to unlock said mobile device for a user to interface therewith; associating said unlock command with said input in said processor; outputting said imaging field of view to said user via a display; outputting to said display a visible two-dimensional virtual object occupying at least a portion of said region; obtaining with said imager at least one image of at least a portion of said field of view with said hand delivering said input in said region therein, and communicating said image to said processor; identifying in said processor a plurality of salient features of said hand comprising a structure of said hand from said input delivered by said hand in said region in said image, said structure comprising a plurality of fingertips of said hand, a plurality of fingers of said hand, and a geometry of said hand; executing said unlock command in said processor in response to said input so as to unlock said mobile device for said user to interface therewith; defining a model of said hand in said processor from said salient features, said hand model comprising said fingertips, said fingers, and said geometry thereof; retaining said hand model; and using said hand model to identify said hand in said processor in subsequent images.
2. A method, comprising: establishing in a processor of a mobile device an imaging field of view for an imager in communication with said processor; defining an input region in said processor within said imaging field of view, said input region being smaller than and substantially fully within said field of view; defining an input in said processor comprising at least one of a hand posture and a hand gesture; defining in said processor an unlock command adapted to unlock said mobile device for a user to interface therewith; associating said unlock command with said input in said processor; outputting said imaging field of view to said user via a display; outputting to said display a visible two-dimensional virtual object occupying at least a portion of said region; obtaining with said imager at least one image of at least a portion of said field of view with said hand delivering said input in said region therein, and communicating said image to said processor; identifying in said processor a plurality of salient features of said hand comprising a structure of said hand from said input delivered by said hand in said region in said image, said structure comprising a plurality of fingertips of said hand, a plurality of fingers of said hand, and a geometry of said hand; executing said unlock command in said processor in response to said input so as to unlock said mobile device for said user to interface therewith; defining a model of said hand in said processor from said salient features, said hand model comprising said fingertips, said fingers, and said geometry thereof; retaining said hand model; and using said hand model to identify said hand in said processor in subsequent images. 4. The method of claim 2 , wherein: said structure comprises five fingertips and five fingers; and said model comprises five fingertips and five fingers.