1. A document verification system for use with a document having at least a portion thereof printed with a predetermined pattern of areas having differences that are not readily detected by the human eye but are readily detected by an optical scanner, wherein the differences represent information regarding validity of the document, comprising: means for scanning an entirety of a face of the document and for producing an electronic graphic image indicative of the entirety of the face of the document as scanned, said electronic graphic image containing said predetermined pattern such that said differences are apparent in said electronic graphic image; and means for detecting a presence and an absence of the differences contained in said electronic graphic image by comparing a density in one area of the graphic image to that in another area of the graphic image, the presence being an indication of the validity of the document, said detecting means including means for searching said electronic graphic image to locate the one area and the another area for purposes of effecting the comparing.