Pattern Matching is actually identifying (Classifying) ID documents by comparing them against a library of known features and designs, to determine whether or not it is genuine.
This methodology works primarily with original documents that are physically scanned using professional scanners.
Pattern Matching is considerably less effective when used with ID document images produced by customers using smartphone cameras, digital cameras and webcams. In such cases, critical parameters such as lighting, focus, angle, fingers on image etc. often prevent reliable matching to a library template.