I think that the reason that some drivers might not want their photograph taken is because they have had some problem with the government (be that a government department / agency, a local authority or the police). Or that they are claiming a benefit of some sort that if it was discovered that they had a job they might well lose that benefit if it was discovered? Or maybe that they have been signed off sick from one employer with a long term illness but have then got a job working for a different employer/