Could someone recommend a free and/or open source GIS application that can orthorectify map images?
INPE in Brazil (National Institute of Spatial Research) has an software called Marlin used for some raster data processing. It's known Marlin can orthorectify, tough I don't know how to proceed. But it's free.INPE also develops the SPRING software. It a GIS suite that can orthorectify and it's free as well.
But unfortunately, those two softwares are not open-source.