The point of this post is to show the incredible amount of detail that can be found in old photographs. A photo's level of detail is always dependent on the printing process that was used to create it. With modern inkjet printers, the most amount of detail that can be printed is about 300 pixels per inch. More than enough to view the photo at arm's length. However, photos printed using traditional silver halide processes (and negatives/slides/film also, of course) can have much more detail in the image. When restoring an old photo, it is very often the case that you should not be afraid to enlarge is, so that the details are brought out.
Oh, and also: Get those kids out of the path of that thresher! I'm afraid they're going to be swallowed up any second now.
I am a full-time photographer and I also own and operate Riveros Photography, here in Toronto. We offer all photography-related services, including printing, framing, etc.