On occasion, the Upper Midwest Environmental
Sciences Center is asked to scan and georeference aerial photography to support
a project. As these data are created they're also placed online so others can
use them as well. Most are served as compressed .sid images, a free image
viewer capable of subsetting, resampling, and exporting the compressed images
to georeferenced TIFF images (a .tif image and a .tfw world file) is available.