Abstract: A matching card game for supermarket contests and other encoding applications utilizes a positive sheet (10), preferably printed in a newspaper, and valid (16) and dummy (12) negative sheets, preferably made available in random order in the store, e.g., affixed to pads, on the wrappings of products, insertions into products, or printed on displays. The valid negative sheet, when placed over the positive sheet in correct registration, produces a recognizable, winning image (18), while similar superimposition of the dummy negative sheet will not produce any recognizable image (14). The sheets are formed by scanning (22) the image (20) to be encoded in a series of parallel adjacent rows. The positive and dummy sheets are printed as a series of rows of monochromatic, random, uniformly-shaped and sized geometric rectangles or other shapes. The negative sheet is similarly printed, except that in the pattern areas, the random rectangles are the inverse of those on the positive sheet in these areas.