1. An image retrieval apparatus for extracting a frame of moving image data as still image data, comprising: a character string input unit configured to input a character string; a reception unit configured to specify a time period based on a user designation; a search unit configured to retrieve frames having the character string input by the character string input unit from moving image data including a plurality of frames; a detecting unit configured to detect a position of the character string input by the character string input unit in a frame of the moving image data; and an image extraction unit configured to extract, when the same position is detected by the detecting unit in each of a predetermined number of frames retrieved by the search unit which are consecutively displayed within the time period specified by the reception unit, one of the predetermined number of frames as still image data.