An image processing apparatus which is capable of merging character strings with an original image without causing garbling. A first storage unit stores first character codes corresponding to a first language in accordance with administrator's input. A second storage unit stores a second character codes corresponding to a second character in accordance with login user's input. A reading unit reads an original image in accordance with login user's input. A generation unit generates a first character image corresponding to the first language on the basis of the first character codes and generates a second character image corresponding to the second language on the basis of the second character codes. A printing unit carries out a printing process based on the first character image, the second character image and the original image.