Georeferenced images in the GeoTIFF format (i.e. TIFF with embedded geographic metadata) can be directly inserted to the proper position in mapping versions of AutoCAD - AutoCAD Map 3D and AutoCAD Civil 3D. Use the map version of the command for attaching images.
If you need to position a GeoTIFF in the plain AutoCAD or AutoCAD Architecture, you can use the free utility CADstudio GeoRefImg. This tool makes use of standalone "world" files with georeferences - TFW, so you need to generate these files first. You can create TFW files from GeoTIFF using the ListGeo tool, part of the LibGeoTIFF library. This free tool can be downloaded from FTP LibGeoTIFF [URL verified 3/2013] or from GeoTiff [URL verified 1/2017]. A TFW file can be generated by running:
listgeo -tfw myimgfile.tif > projreport.txt
Then you can use GeoRefImg to reposition your image to its right position (georeference).
Another option for exporting world files is the free utility GeoTiffExaminer.