Aunt Ruth and the outlaw

During the latter part of the 19th century and early part of the 20th, you could go down to your local photographer with a picture and he'd make it into postcards. The picture above was a postcard, though it was never sent through the mail. Seated on the horse is my grandmother's aunt Ruth. This is my Dad's side of the family.
On the back of the postcard is written,"This is Ruth and that notorious outlaw Frank James - a young man she had been keeping company with. He is in Mo. [Missouri] now."
The scene (adobe house and windmill) suggest New Mexico, but dad was born in Glenelder, Kansas, and I think that's a more likely possibility.
If it is indeed Frank James, the time would have to be about 1870. That would fit with the chronology of the family.