1. An image processing apparatus, comprising: an image reading unit configured to read information as image data; a character recognition unit configured to recognize individual characters included in the image data; a grouping unit configured to group the individual characters recognized by the character recognition unit into one or more character strings based on character information indicating a format of the character; a character extraction unit configured to extract a character string for which a link is to be created based on an importance of the character string obtained by the grouping; a character search unit configured to search the image data in which the characters have been recognized for the character string having the same character base among the character strings extracted by the character extraction unit; and a link setting unit configured to link the character strings having the same character base that are retrieved by the character search unit, to each other based on the importance.