1. An image processing apparatus comprising: an extraction unit configured to extract a first character string appearing on a first image, and a second character string appearing on a second image; a determination unit configured to determine that both a subject of the first character string and a subject of the second character string correspond to a first subject; a cut-out unit configured to cut out each of characters constituting the first character string, in units of a character, and to cut out each of characters constituting the second character string, in units of a character; a calculation unit configured to calculate a first similarity degree group which is composed of similarity degrees between the respective characters constituting the first character string and respective candidate characters in a candidate character group, and to calculate a second similarity degree group which is composed of similarity degrees between the respective characters constituting the second character string and the respective candidate characters in the candidate character group; and a recognition unit configured to recognize a character string of the first subject, based on the first similarity degree group and the second similarity degree group.