An apparatus and method for checking value documents, in particular bank notes, and a value document processing system having at least one sensor for capturing an electromagnetic radiation transmitted by a value document and generating corresponding transmission signals, and an evaluation device for checking whether the value document has a foreign object taking into account the transmission signals. From the transmission signals an edge course of the value document is derived and a rectangle is approximated to the edge course. By comparing the edge course of the transmission image with the rectangle, the presence of a foreign object such as an adhesive tape, can be ascertained.