1. An information processing device comprising: an image database for storing an image as a search target; character string region extraction means for extracting a character string region including a character string in the image stored in the image database; character string recognition means for recognizing the character string in the character string region extracted by the character string region extraction means; visual saliency calculation means for calculating and storing a visual saliency of the character string based on at least any one or more of a size, a color, a shape, and a decoration of characters forming the character string, and a contrast between a character color and a background color, from an image of the character string region extracted by the character string region extraction means; search keyword input means for inputting a search keyword; search means for performing a search to determine whether the keyword input by the keyword input means matches at least a part of the character string recognized by the character string recognition means and for calculating a score value of the image including the character string, from the visual saliency of the character string region from which the matching character string was recognized; and output means for sorting and outputting the result of the search by the search means, according to the score value calculated by the search means.