1. A form image managing apparatus, comprising a processor configured to execute a process including: obtaining a master image; partitioning the obtained master image; storing partitioned images obtained by partitioning the master image as partitioned master images; obtains obtaining an image of a form; searching the stored partitioned master images for a partitioned master image having a high correlation with each of a plurality of partial images obtained by partitioning the image of the form; generating difference data between the partial image and corresponding partitioned master image having the high correlation with the partial image; and storing, as form image data that represents the image of the form, identification information for identifying the partitioned master image having a high correlation with the partial images and the difference data by being made to correspond to each of the partial images.