Highway tickets treated with ninhydrin, solution for thermal paper.
(a) Ticket before the treatment;
(b) ticket after the treatment viewed in the visible region. In this
case, because of the particular used solution, there is no black stain on the ticket;
(c) inspection performed by exploiting the luminescence of the thermal paper (input
radiation: 400–640 nm, longpass filter on the emitted radiation: >695 nm);
(d) revealed fingermarks.