Lieutenant-General Gerhard "Gerd" Barkhorn (20 March 1919 – 8 January 1983), was the second most successful fighter ace of all time after fellow Luftwaffe pilot Erich Hartmann. Barkhorn flew 1,104 combat sorties and was credited with 301 victories on the Eastern Front against the Soviet Red Air Force piloting the Messerschmitt Bf 109 and Focke-Wulf Fw 190D-9. He flew with the famed Jagdgeschwader 52 (JG 52—Fighter Wing 52), alongside fellow aces Hartmann and Günther Rall, and Jagdgeschwader 2 (JG 2). Despite being the second highest scoring pilot in aviation history, Barkhorn was not awarded the Diamonds to his Knight's Cross with Oak Leaves and Swords after achieving his 300th victory on 5 January 1945.
Sources: unknown Internet stes. Will post some from some books I have later.
Two different aircraft. Look at the chevron differences too. Sundin's appears to be depicting the aircaft in your photo with the signatures on it. Note the small intake under the windscreen which does not appear in the other 109's.
"This aircraft has been very often mistakenly labeled as a G-5 but this machine is obviously not lacking the pressure bulkhead and silica tablets. Plus the fresh air door on the side. The G-5s were often issued to home defence units when the high altitude pressurized aircraft was needed. Most Eastern front air battles were flown at low and medium altitude." FalkeEins - the Luftwaffe blog: Bf109 G-6 of Hptm Gerhard Barkhorn JG52