You can't automatically georeference imagery. You need to tie it into key points. Unless you have a coordinated bounding box for the image (which is kind of like a georeference any way).
If your images are georeferenced and you want to ortho-rectify (meaning, remove terrain distortions) then I think it will be a little tricky, but see here for open source ways.
If you just want to georeference a bunch of images, you can do that in QGIS quite efficiently. Here's a tutorial, though it doesn't look great. Since you've got existing imagery for the area, set up a QGIS workspace with that in it, so you've got some known points. Then load each image you want to georeference up in turn and use the georeferencer tool. It'll take time, but there's not automated way to do it.