John, OSSIM has a command-line tool that might be helpful. It is called "extract_vertices" and outputs the 4 corners of the true image data.
Here is an excerpt from the document - Used to compute the valid vertices (corners) of an image. Defines a polygon - inside the polygon are valid sampled pixels outside are nulls. extract_vertices <image_file> You may need to install OSSIM to get the command-line tools. http://download.osgeo.org/ossim/ Keith
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