Barnum & Bailey Circus Poster

Q: This Barnum & Bailey circus poster has been in my husband’s family for as long as he can remember, and he’s 68 years old. But he doesn’t know how old it really is. It’s 35 inches high and 43 inches wide. The poster was rolled up in a tube until the mid-1970s when his dad gave it to him, and he had it covered with Plexiglas and framed. The poster pictures the Wild Beast Division in a street parade. On the bottom it says “Strobridge Lith Co Cinti N.Y. & Lod,” I took the poster out of its frame and found it was glued to thin cardboard. There are lots of holes in it where metal brads held the picture into the frame. How can I tell if this is an original poster? What is it worth and how can we sell it?