Jack Dunn was born in 1872. That is before baseball gloves. By the time he's playing ball gloves are around, but are rare, and not used by hard core base ballists. Dunn made it to what we now consider the major leagues with Brooklyn in 1897.
I'm confident that it is a vertical image. I think some of the horizontal-heads see that and are just stirring, and some really don't see it. I can envision a ball player getting in that position for a ball he's going back for that was popped over his head at third or short, I can see a fellow getting into that position going for a fly near the edge of a railing beside the stands. This T210 of Chandler now on eBay OUT OUT OUT, be OUTED card!!!
http://cgi.ebay.com/ws/eBayISAPI.dll...STRK:MEBIDX:IT ends in a few hours, and I think that its high price is due to the similarity of the Dunn image. AND, I think that ball players who learned to play without a glove, as Dunn would have, were likely to have caught balls like that more often than some 21st century product from the sunshine of California or Florida.
As I out Chandler, he's at $50.99. I think he'll sell for much more than that. I don't know if a vertical-head is going to bid it up, to further the cause of Dunn being a vertical card; or if it will be bid up by a horizontal-head who plans on burning the card so no one will see how similar Dunn is...