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Posted By: davidcycleback

It's called cyanotype (cyan = blue). The photos aren't tinted, but are blue and white (instead of black and white). It's an old time process, popular in the 1800s and early 1900s. It is used today in fine art photography. There are a fair number of early 1900s baseball cyanotypes, and, without seeing them in person, it's fair to assume that yours are vintage.