[drcy]

Many old original have blank backs, including snap shots and Hollywood movie stills. Though it is always nice to have a stamp of some sort. You just have to be more competant at photo dating.

Beyond cabinet cards and such, which by original design are supposed to have a backing, it is harder to authenticate photos glued to backing. But you can often be confident it is vintage anyway. Antique photos often have physical deterioration signs that show it's old. If you are talking about cabinet cards and CDVs, they certainly can be authenticated, and there are various methods for authenticating. That's different that a later photo that someone glued to a piece of cardboard-- which sometimes happened with news photos.

Obviously it is nice to have a photographer's, photo service's or such's stamp or tag on back. That makes things more straight foreword and most collectors would prefer it. If the photo is supposed to be a famous photographer, you'd want his stamp on back.

One thing is with an online sale or auction, you don't have the photo in hand to inspect and the stamping can a great aid. That's what is so nice about stampings and tags.