Frees, Harry Whittier (1879–1953)

According to Wikipedia

Harry Whittier Frees (1879–1953) was an American photographer who created novelty postcards and children's books based on his photographs of live, posed animals. He dressed the animals and posed them in human situations with props, often with captions; these can be seen as progenitors of modern lolcats.

There's no doubt Frees went to a lot of trouble to convince people that the pets were live. See, for example, the ad for "Photographing Animal Pets" on the first page of Kitty's First Day at Catnip School. But I don't buy it. Have a look for yourself, particularly at the paws and the awkward way they are frequently bent. He was working with stuffed animals.