1. A compact, mobile apparatus for iris image acquisition, adapted to address effects of ocular dominance in the subject and to guide positioning of the subject's iris for the image acquisition, the apparatus comprising: a sensor for acquiring an iris image from a subject; and a compact mirror oriented relative to a dominant eye of the subject, and sized to present an image of a single iris to the subject when the apparatus is positioned at a suitable distance for image acquisition, to assist the subject in positioning the iris for iris image acquisition, the mirror positioned between the sensor and the iris during iris image acquisition, and transmitting a portion of light reflected off the iris to the sensor.