1. A method of operating an image-based check processing system to detect a double feed condition of document items, the method comprising: reading one magnetic ink character recognition (MICR) codeline from a first predefined area of an image of a document item; based upon the read of one MICR codeline from the first predefined area of the item image, determining if the document item is a carrier envelope; concluding that the document item is not a double-fed item when a determination is made that the document item is a carrier-envelope based upon the read of one MICR codeline from the first predefined area of the item image; concluding that the document item is potentially a double-fed item when a determination is made that the document item is not a carrier envelope based upon the read of one MICR codeline from the first predefined area of the item image; reading one MICR codeline from a second predefined area which is different from the first predefined area of the item image; based upon the read of one MICR codeline from the second predefined area of the item image, determining if the item image has a valid MICR codeline; concluding that the document item is not a double-fed item when a determination is made that one valid MICR codeline has been read from the second predefined area of the item image; concluding that the document item is potentially a double-fed item when a determination is made that one valid MICR codeline has not been read from the second predefined area of the item image; and alerting an operator to indicate a potentially double-fed item when a determination is made that document item is not a carrier envelope based upon the read of one MICR codeline from the first predefined area of the item image and a determination is made that one valid MICR codeline has not been read from the second predefined area of the item image.