1. An image processing apparatus comprising: a recognition unit that recognizes a layout of a line including a character string in an image read from an original; a determination unit that determines a size of a region in which additional information is to be embedded so as to include at least a part of a line including a character string in the region, based on the layout recognized by the recognition unit; a dividing unit that divides the image read from the original into equal regions having the size determined by the determination unit; an embedding unit that embeds the additional information in the image divided by the dividing unit; and an adding unit that adds information for error correction to the additional information, wherein the embedding unit scans a group of regions, the number of which corresponds to an amount of the additional information and the information for error correction, searches for a position of the group of regions in which the number of regions not including a character or a part of a character is within an error-correctable number in the group of regions, and embeds the additional information in a region including a character or a part of a character in this position.