NeoMedia Technologies, Inc (NEOM)

[Elementus]

To identify user you need to pass user id to server together with url or encoded index, or use cookies. First method depends on reader, second on user's wish not to delete or allow cookies. Both methods are not reliable.
i think they either deliver custom web solutions to their clients or direct users to own site for processing before redirection to products.
Much cheaper and more reliable to use proprietary resolution service and force other readers transfer information you need but not relay on good will or other conditions. I am sure NEOM use right way.