1. A form image managing system, comprising: a master image obtaining unit which obtains a master image; a partitioning unit which partitions the obtained master image; a partitioned master image storing unit which stores partitioned images obtained by partitioning the master image by the partitioning unit as partitioned master images; a form image obtaining unit which obtains an image of a form; a searching unit which searches the partitioned master image storing unit 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; a difference data generating unit which generates difference data between the partial image and corresponding partitioned master image having the high correlation with the partial image; and a form image data storing unit which stores, as form image data that represents the image of the form, identification information for identifying the corresponding partitioned master image and the difference data generated by the difference data generating unit by making the identification information and the difference data correspond to the partial image.