A postcard collector, with more than 11,000 of them to his name, suddenly noticed something odd about many of the vintage ones. Whether photos of Alberta, California, Juarez or anywhere else, they all had the same sky. [via Metafilter]
Dexter Press was once one of the largest publishers of "chrome-era postcards" — postcards made from color photographs became popular in the 1940s. By the time James started collecting in the 1980s, "chrome cards" were mostly overlooked by collectors, and could be bought cheaply in flea markets. It wasn't until he looked through a lot of these cards that he noticed the same sky repeating itself.
The tl;dr: it was laborious manual "photoshopping" in the pre-ditigal era to "improve" images, all accomplished by Dexter, a genuine pioneer of color fidelity, print quality and print volume in the post-war postcard biz. There's a lot more of the same sky to be found on flickr.