This isn't your father's John Deere, that's for sure. This is an old steam traction engine. Too big and too heavy to be very mobile on soft soil, it was often strategically located on (or near) a farm field and its engine used to move or drive other equipment. Sometimes two of these behemoths were used... one pulling a plow to one side of a field and another pulling it back the other direction. I'm not a farmer, but these farm workers may have been using the steam engine to drive a wheat thresher which is out of the photo. Whatever they were doing at the time, they've been immortalized in this old AZO real photo postcard from the 1904 - 1918 time period.
The area pictured is as flat as Felton,Delaware so the photo may have been taken around these parts (Lower Delaware, Maryland Easter Shore). I think this old contraption may be a Case Corporation or a Peerless steam tractor, but I've not been able to find a match. If you recognize this old beauty, please leave a comment to identify it for us. Other possible manufactures may include Best Manufacturing, Ransomes, Fordson, Advance Rumely, Peerless, and Deering Harvester.
ADDED January 22, 2007: Thanks to some good advice from our friends at Yesterday's Tractor Magazine, this old tractor is very likely a Peerless steam traction engine, manufactured by the Geiser Manufacturing Company of Waynesboro, PA.