Hi, I recently scanned a paper photo and then opened it in Photoshop. When trying to do a bit of dodging/burning it would not work. Am I doing something wrong, or is it that one can't edit scanned images?
You're doing something wrong. Is the file a JPG? If it's a GIF or TIFF or BMP it's possible that photoshop may not be able to do some types of editing.
GIF files have a very limited color palette (256 values) and so you really can't dodge and burn them since you can't make subtle changes of color.
If it is something other than a JPEG, just open it up and then save a copy as a JPEG and work on that.