What are proposed are a method and a system for guaranteeing the authenticity or checking the authenticity of documents, in particular banknotes or the like, which each have a substrate (1) with specific substrate features (2), an image of the substrate being recorded before a document is issued and the image data obtained in the process being stored in a manner assigned to document data, in order to keep these data ready for possible later comparison enquiries concerning the authenticity of an issued document.