17. The mobile device of claim 16 wherein: the predetermined test uses at least one peak in a profile obtained by projection of intensities of pixels along a direction, wherein a property of the at least one peak satisfies a predetermined condition identified in the predetermined test.
17. The mobile device of claim 16 wherein: the predetermined test uses at least one peak in a profile obtained by projection of intensities of pixels along a direction, wherein a property of the at least one peak satisfies a predetermined condition identified in the predetermined test. 18. The mobile device of claim 17 wherein the processor is programmed to: binarize a plurality of pixels, within a row among a group of rows in the first block, by assigning thereto one of two values, based on comparison of intensities of said plurality of pixels with a threshold determined by use of intensities of multiple pixels in the first block; and count within the row, a number of pixels having said common value, to identify the at least one peak in the profile.