An image-based check processing system has a focus test pattern on a background surface which is disposed along one side of a document transport path. An imaging camera is disposed along an opposite side of the document transport path and faces the focus test pattern. The imaging camera captures an image of a financial document along the document transport path when the financial document is between the imaging camera and the focus test pattern, and captures an image of the focus test pattern when no financial document is between the imaging camera and the focus test pattern. An energizeable first light source of a first electromagnetic frequency is provided for, when energized, illuminating a financial document moving past the imaging camera to allow the imaging camera to capture an image of the illuminated financial document. An energizeable second light source of a second electromagnetic frequency is provided for, when energized, illuminating the focus test pattern to allow the imaging camera to capture an image of the illuminated focus test pattern. The first light source is controlled so that the first light source is energized when a financial document in the document transport path is between the imaging camera and the focus test pattern. The second light source is controlled so that the second light source is energized when a gap is between adjacent financial documents in the document transport path. The captured image of the focus test pattern is analyzed to determine if the focus of the imaging camera is acceptable.