[thecatspajamas]

I've always been under the assumption that most photographers' stamps were 1) to help ensure they got paid when the photo was used and 2) as a form of advertising should anyone happen to like the photo and want to purchase additional prints.

At least two of the stamps also feature his mailing address, which changed as he moved, which would explain those changes.

Added: Henry's book shows 3 varieties, 2 of which have an address and are dated to the 1910's. The example of his Englewood NJ addressed stamp also shows his New York addressed stamp scribbled out, so presumably he moved from New York to New Jersey at some point in the 1910's. He also shows the "Evening Telegram" variety which he dates to 1912 (I guess he only used it for 1 year?) He was active up through the 1930's though, so I don't know how he stamped his work in those last 2 decades (I've not researched it myself, so this is all from the book or assumptions based on it).