A device and a system for detecting a tape or a piece of glue on a document and methods for detecting a tape or a piece of glue on a document are described. The device comprises at least one light source, at least one light receiver and at least one light barrier. The at least one light source is arranged on a first side of the at least one light barrier and the at least one light receiver is arranged on a second side of the at least one light barrier opposite to the first side. The light barrier is configured to come into contact with a document to prevent or reduce light emitted from the light source on the first side of the light barrier to be transmitted to the light receiver on the second side of the light barrier.