Good lord. Just stumbled across this:
https://cdnc.ucr.edu/cgi-bin/cdnc?a=...9080829.2.82.7
When I looked at the inscription, and then looked at the photo stamp, I noticed they both said Joe O'Connor.
Put O'Connor and Ketchel into Google and this popped right up.
Ketchel's manager for a bit, but also a photographer by trade. The photo is actually of O'Connor according to the newspaper article I linked to.
Amazing that fighter and manager looked so much alike.
It was all actually right there in the photo. I was mistaking the inscription. I thought it said "My Stanley Ketchel". It actually says "Mg (manager) Stanley Ketchel.