The present disclosure describes projecting a structured light pattern onto a surface and detecting and responding to interactions with the same. A method includes-acquiring an image based on light reflected from a vicinity of the projection surface, and identifying regions of the acquired image that correspond to a feature that is within a specified distance of the projection surface by identifying regions of the acquired image for which intensity data differs relative to other regions of the acquired image and which fit a specified homographic relationship with respect to corresponding regions of a reference image.