An optical card reader for reading marks made on the face of a preprinted card utilizes a video camera and a memory device to capture and store an image of at least a portion of the card. Positioning indices are printed on the card, and the reader has stored therein information defining possible locations of valid marks relative to the positioning indices. The centroids of the positioning indices on the cards are determined to define the possible locations of valid marks on the cards. The densities and centroids of the marks located in the possible locations are analyzed to determine if a valid mark is present.