Apparatus that includes a communication interface capable of communication with a management entity over a network; a biometric module adapted to acquire an image of a skin-covered body part submitted thereto; an output device; and a processing unit. The processing unit is adapted for releasing a prompting signal via the output device, the prompting signal prompting submission of a skin-covered body part at the biometric module. Furthermore, responsive to acquisition of an image by the biometric module further to releasing the prompting signal, the processing module is adapted for producing a candidate code based on geometric measures of respective combinations of pixels taken from a plurality of subsets of like-shaded pixels in the image. Finally, the processing module is adapted for releasing the candidate code via the communication interface for comparison at the management entity with an expected code, thereby to verify presence of a person associated with the expected code.