1. An image processing apparatus comprising: a first interface configured to receive a first image from a first external apparatus; a second interface configured to receive a second image from a second external apparatus, wherein the first image is different from the second image; and a processor configured to: extract a first character string appearing on the first image, and a second character string appearing on the second image; determine that both the first character string and the second character string correspond to a photographed subject in the first image and second image; cut out each of the characters constituting the first character string, in units of a character; cut out each of the characters constituting the second character string, in units of a character; 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; 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 recognize a character string of the first subject, based on the first similarity degree group and the second similarity degree group.