1. An image forming system, comprising: a target-log-image extracting unit configured to extract a log image, as a target log image likely to have been generated by use for a specific purpose of an image forming apparatus, when text information extracted from the log image of the image forming apparatus by optical character recognition includes a specific phrase; and a relevant-log-image extracting unit configured to extract a log image similar to the target log image, as a relevant log image, based on a specific feature of the target log image extracted by the target-log-image extracting unit.