A processor is provided with first and second document images. The first image represents an instance of a reference document to which instance a mark has been added. The second image is selected from among a collection of document images and represents the reference document without the mark. The processor automatically extracts from the first document image a set of pixels representing the mark. This is done by performing a reference-based mark extraction technique in which the second document image serves as a reference image and in which substantially the entirety of the first document image is compared with substantially the entirety of the second document image. Also, the processor is provided with information about a set of active elements of the reference document. The reference document has at least one such active element and each active element is associated with at least one action. The processor interprets the extracted set of pixels representing the mark by determining whether the mark indicates any of the active elements of the reference document. If the mark indicates an active element, the processor facilitates the action with which the indicated active element is associated.