Miller's ranch, "Jack and I"

A photo of Miller's ranch, "Jack and I" - this is one of the three I know to be associated with the Miller's ranch in Colorado. the only thing written on the back was Jack and I. Who the man is, ? and estimated year range 1906 - 1915, but that is an estimate, not an absolute.

Miller's ranch in Colorado, probably near Watkins, Adams County... do you recognize the man, or know anything about the Millers?