An apparatus receives a document image and digital-watermark information
and determines an embedding capacity based on a number of the letters in
the document image. The apparatus determines whether or not the entire
digital-watermark information is capable of being embedded in the
document image based on the determined embedding capacity and embeds the
digital-watermark information in the document image based on a result of
the determination of whether or not the entire digital-watermark
information is capable of being embedded in the document image.