Abstract: The present invention is directed to a system that ensures one-by-one processing of incoming check image files. The system receives incoming check image files and inputs them into a queue for processing. An application server (e.g., a thread) then selects one check image file from the queue for processing. For example, the system may process the check image to extract check information from the check image file. Once selected by the application server, the check image file is “locked” so that no other thread is enabled to select the same check image file. In this way, the system of the present invention is configured to ensure that each check image file is processed only one time.