You can see it in more detail, along with a fairly heated discussion about whether money should be spent on a headstone for a dog, at this link.
I'm sure it surprises no one that people are paying tribute to deceased pets. We've talked before about the debate over being buried with your pet.
But it's great to see an actual photograph documenting the interest. I love that it's such a social occasion—several friends have gathered, bringing their dogs along, all to mourn "Buster" together. And I love knowing that the modern American obsession with dogs is at least 90 years old.