Move photos back to Apple Photos from SSD

Several months ago, I thought that I would try to be done with Apple photos and just use Google photos. At that time I manually downloaded all the photos in my Apple photos and sent them to an SSD. I have figured out that I don’t like Google photos near as much as I like Apple photos. I would like to bring those photos back into Apple photos, but I want to make sure that they are not going to come in as duplicates. Is that possible? If so, how would I do that?