The capo looks "commercial," and much like some common now. There might be documentation that would help date the image more accurately if someone can get a "make" on it. Guitars weren't patented usually, only details for them. The capo would likely have been a patented "in-the-whole" design(?) and production dates/info might have been dug out by someone with a website.

The capo shows reasonable detail. There's no visible marking on the head that I can see, in the 300DPI "larger image" at ebay. The ebay image likely shows all the detail that was in the original, since long exposure times generally led to "very soft" lenses in tintype portrait days so that motion blur didn't show too prominently.

John