IDENTIFICATION AND PROTECTION OF SECURITY DOCUMENTS

The present invention provides methods and systems that are helpful for authenticating or protecting physical and electronic documents like financial documents and identification documents. One claim recites a method including: receiving digital data corresponding to a physical document; transforming the digital data into a frequency domain; comparing characteristics associated with the transformed digital data to predetermined characteristics that are associated with a first document type, and if the characteristics coincide, determining that the physical document is of the first document type; and if the characteristics do not coincide, comparing the characteristics of the transformed digital data to predetermined characteristics that are associated with a second document type, and if the characteristics coincide, determining that the physical document is of the second document type. Of course, other claims and combinations are provided as well.