US Patent 7220524 System and method for producing secure toner-based images

A system and a method for printing a secure document that is difficult to forge and readily easy to visually verify are disclosed. The system includes a colorant for printing an image on a surface of a document, a dye for forming a latent version of the image underneath the surface, a substrate, and a migration agent for facilitating the migration of the dye through at least a portion of the substrate. The migration agent may be coated onto a portion of the substrate or embedded within the substrate. An ink may serve as the migration agent, in which case, the ink contains a solute for the dye.