One stray dog found in Greenville, S.C., has posed quite a mystery for the local animal shelter that took him in.

Although pictures are usually "worth a thousand words," in the case of this 2-year-old pit bull who was brought into Greenville County Animal Care on Jan. 13, the old black-and-white photo found mysteriously tucked into his collar has done nothing but elicit questions about the pup's unexplained past.

"It's a really small photo, it's black and white, of a man leaning against a gate post or a railing," Susan Bufano, the shelter's media relations coordinator, told GoodMorningAmerica.com. "Who knows what the story is with this."

The stray pit bull, affectionately named Soldier by the staff, has no microchip or identification tag to help the shelter locate his potential owner, if he even has one.

But the aged, antique photo of what looks like a soldier casually posing for the camera was obviously tucked into the dog's black canvas collar by someone at some point, but by whom, when or why remains to be seen.

"It is really interesting," said Bufano. "I was asking the staff if they have ever seen this before, but no. A dog came in once with a cape on, a very shy dog, but we've never had anything here like this."

Even the collar Soldier was found wearing is different from what the shelter typically sees.

"It's a really wide collar, canvas, and it's got an opening," she said. "I can't imagine this photo made it in there on accident."

The shelter has gotten plenty of phone calls and comments since it posted Soldier's mysterious story on its Facebook page, but so far, no leads and no explanation.

"It's very weird," said Bufano. "Someone might not even want this dog back but may have forgotten they put this photo in there. It's sad because this photo definitely means something to someone."