The present invention decides whether an OCR processing is necessary or not for a printing job by using a difference between text data extracted by performing the OCR processing on an image generated based on a previous printing job having been processed previously and text data extracted from text drawing command of the previous printing job having been processed previously. If the OCR processing is decided to be unnecessary, the text data extracted from the text drawing command of the printing job is registered in a database for retrieving an image data. If the OCR processing is decided to be necessary, text data extracted by performing OCR processing on the image data generated based on the drawing commands of the printing job and the text data extracted from the text drawing command of the printing job are registered in a database for retrieving an image data.