I've seen date stamps before the 1930s.
As far as pricing goes, it depends what you buy and what you pay. People overpay and underpay for photos, so I can't promise anything on a specific theoretical photo. If, in a bidding war, you pay $500 for a $50 photo, I'm certainly not going to guarantee it's worth $500 in five years. A sad fact of today's hobby is people shill their auctions, and prices are realized prices are too high right now. Show me a specific photo and I'll tell you if I think the price was good. Buy quality originals at good prices. Don't jump on bandwagons (as with everywhere else, the hobby has fads), buy quality, know quality. You learn quality and rarity and pricing by following auctions and looking at photos. It's not something you can learn in a five minute lesson.
I think some stuff goes too high these days, but I also see many quality photos that I think are good bargains today. Some old display photos and display composite photos I think are undervalued or at least at good fair prices. Don't look just at news photos-- look into cabinet cards, panoramas, early display photos, tintypes, etc. News photos are plentiful, while the other areas contain many rarities. I thought many photos in the Legendary Dreier auction were undervalued.
I think the majority of collectors are undereducated and myopic, and simply follow hobby trends and fads. There are rare items that are undervalued because the majority of collectors aren't educated or experienced enough to realize the rarity. Collectors don't get wealthy from artifact investments by following latest trends and fads, but by knowing buying quality and rarity before the rest of the hobby realizes the quality and rarity.
I do think, looking overall at all the photos and not zeroing on one or two, past auction house results are a fair indicator of price. As I said, a specific photo may have been bought at a bargain while another went too high, so look overall at all the photos.
My guide to photos pdf ebook (long download time)