I would say if there are photos you are really concerned about create a physical instance of them. Print them out," he continued.
Cerf is talking about an issue anyone who has kept up with changing technology over time has struggled with: A document stored on a floppy disk is little use now because software can't read the old file and the fonts are no longer around. And you'd only discover those problems if there's a computer around that will still take a floppy disk.