1. A scan server comprising: a creation unit configured to create instruction data for instructing a scan setting and OCR preprocessing to be performed by a scan device; a transmission unit configured to transmit the created instruction data to the scan device; a reception unit configured to receive, from the scan device, an OCR-preprocessed scan image which is acquired by performing the scan setting and the OCR preprocessing instructed by the instruction data in the scan device; an OCR unit configured to perform an OCR processing on the received OCR-preprocessed scan image; and a scan device information storage unit configured to store OCR preprocessing which can be performed by the scan device, wherein the creation unit acquires the OCR preprocessing which should be performed before the OCR processing from the OCR preprocessing information storage unit; acquires the OCR preprocessing which can be performed by the scan device from the scan device information storage unit; and describes, in the instruction data, only the OCR preprocessing which can be performed by the scan device among the OCR preprocessing which should be performed, and the OCR unit performs, before performing the OCR processing, OCR preprocessing which is not described in the instruction data among the OCR preprocessing which should be performed.