1. A device for efficient free-space finger recognition, the device comprising: a base; a vertical member, a lower portion of the vertical member affixed to the base; a head affixed to an upper portion of the vertical member, the head comprising a depth sensor arranged to have a downward field of view; and a hardware circuit implemented hand discriminator to: identify a surface in a depth image captured by the depth sensor, the surface being a base plane in a viewing frustum derived from the depth image; identify one or more blobs in the depth image, a blob in the one or more blobs comprising a plurality of contiguous pixels in the depth image that are closer to the depth sensor than the surface; and for each blob in the one or more blobs: determine if the blob intersects an edge of the depth image including the hand discriminator to create a mask corresponding to the depth image by: adding a predetermined number of pixels from each edge of the depth image to the mask; and adding the pixels of a blob to the mask when a pixel of a contour of the blob corresponds to an existing pixel of the mask; and classify the blob as a potential hand if it does intersect with the edge and classify the blob as an object otherwise, the classification based on whether the blob is within the mask.