I am creating an exercise for remote sensing students and would like to take an existing raster and remove the spatial reference from the file so that the students can practice using another image to orthorectify the first. I am using ArcGIS 10. Any hints?
The fastest way to do this is to just delete the files that supply the spatial information related to the raster. If the image is stored as a tiff or you can just open up the folder it's stored in and delete all the files except the actual image. Then give that file to the students.
Looking at the image below, you would delete everything except the highlighted file, then distribute that.
I'm not certain how this would work with other raster formats that encapsulate the spatial information but you could always just export them to a tiff and then use this technique.
Another way that will completely strip any internal GeoTiff tags is by using the GDAL gdal_translate utility to convert the tif to a baseline tiff.
I realise you are using ArcGIS, so do I, but I have found GDAL to be another valuable tool in my geospatial software toolbox. Precompiled GDAL binaries can be downloaded from the GISInternals website.