antique military button found in a shell - authentic or fake?

we found this seemingly antique military button attached to the inside of a conch shell that's been in our family awhile. I haven't touched it up at all, and don't have any expectations that it's of value, but would like to no if authentic or not. tried an image search on google, and came up with a stock photo (http://www.alamy.com/stock-photo-antique-silver-buttons-with-the-emblem-of-the-military-uniform-98265176.html) but no explanation of the button type or history. think the front is silver, nut the back is too rusted over to make anything out. thoughts/suggestions?