I use iCloud Photo Library. That's not the same as iCloud Drive, but it does count against your iCloud Storage.
I often upload photos to Flickr, as a kind of backup. I haven't been good about keeping up with that lately; mostly because the way iCloud Photo Library is working. I have it synced with Photos on my Mac with the keep originals on machine option turned on. Since the Mac is backed up in two places (one local and one online) I'm feeling fairly secure about my library.