1. A method for embedding information in a printed image, the information being represented by positions of dots which are to be superimposed on a document image and be printed on a sheet together with the document image, the method comprising: embedding, in the document image according to a first information expression rule, a first embed-image including first dots; and embedding, in the document image according to a second information expression rule different from the first information expression rule, a second embed-image including second dots; printing the document image, including the embedded first embed-image and the embedded second embed-image, on the sheet; wherein, after the printing, positions of the first dots on the sheet represent first information, positions of the second dots on the sheet represent second information, and at least a part of the first embed-image and a part of the second embed-image exist in the same region on the sheet.