The signature has been given a 9 out of 10 grade ... while Christie's officials say the photo -- which features Jackson throwing a ball at spring training in 1911 -- has "minimal surface wear and no mentionable defects."
The picture had previously sold at auction back in 2015, going for just $179K.
Of course, the piece is also super valuable because Jackson is considered arguably the best -- and most infamous -- baseball player of all-time.
He batted .356 in his 13-year career ... but was also banned from baseball in 1921 for his alleged role in fixing the 1919 World Series.
No word yet on who the buyer or the seller of the photo was ... but congrats to both on the historic transaction.