I have all of my 450 classmates' high school graduation photos ready to upload for their "Then" photo. However I am struggling to see how to upload the photos via bulk upload. Certainly not wanting to do them one by one. Am I just not seeing something obvious? Hope so. All suggestions are much appreciated. Thank you.

Well, first off, classmate's graduation photos normally would be uploaded to their "YearBook" photos. "Then" photos are usually uploaded by the classmates themselves.
And unfortunately, as often as this has come up over the years, to my knowledge there is still no "bulk upload" feature or option for member photos. It took over a week for my co-admin and I to scan and upload all the yearbook photos for our class - and it's a relatively small class of 150.