You will find the borders in degrees in the enclosed html file. gdalinfo can give you the same values, but these are the corners of the tif including the legend, not the map canvas you are interested in. Unfortunately, the map is in a lcc projection, and thus the borders do not follow the exact degree of latitude and longitude, and are not even rectangular.
So you have to create a cutline shapefile using QGIS manually. The shapefile should have the same CRS as the tif file.
- Load the tif file into QGIS. I took Albuquerque North as reference. A custom CRS will be created
- Set the project CRS to that of the layer
- Create a new polygon shapefile, choosing the custom CRS from the first step
- Draw a polygon around the map content
- Adjust the corners by zooming in if necessary
Raster -> Extraction -> Clipper to create a new tif file, with nodata set to 0, and the polygon shapefile as mask layer. The command line will look this way:
gdalwarp -dstnodata 0 -q -cutline D:/Karten/shp/Länder/USA/AlbuqN_extent.shp -crop_to_cutline -of GTiff "D:\\Karten\\shp\\Länder\\USA\\Albuquerque 92 North.tif" D:/Karten/shp/Länder/USA/AlbuqN.tif
You have to do that once for every map, and can then use gdalwarp with that commandline indepently from QGIS for future downloads of the same map.