A system electronically registers an image on an input document. The system includes a scanner for generating an image data stream representing an electronic image of the image on the input document and an edge detecting circuit for detecting edge data within the image data stream. A circuit detects a first corner of a leading edge of the input document based on the detected edge data and for establishing a first coordinate value therefrom and a second corner of a leading edge of the input document based on the detected edge data and for establishing a second coordinate value therefrom. The system further determines a minimum and maximum location for a leading edge of the scanned document and determines a minimum and maximum location for a trailing edge of the scanned document. An image window is generated representing valid image data to processed and rendered based on the minimum and maximum location for a leading edge of the scanned document, the minimum and maximum location for a trailing edge of the scanned document, the first coordinate value, and the second coordinate value.