From left to right: Generalfeldmarschall Wilhelm Keitel (Chef der Oberkommando der Wehrmacht), Adolf Hitler (Führer und Oberster Befehlshaber der Wehrmacht), Oberstleutnant Fritz Claus (Leiter referats IV in der Inspektion 5, Festungswesen, im Oberkommando des Heeres), and General der Pioniere Alfred Jacob (General der Pioniere und Festungen im Oberkommando des Heeres). This photo was taken when pioneer general Jacob showed Hitler the latest German fortification and bunker designs, which would later be used on many battle fronts. There is no information when and where this photo was taken, but most likely in June 1943, shortly after Jacob was awarded the Ritterkreuz des Kriegsverdienstkreuz mit Schwertern (June 4, 1943), the medal attached to his neck. Other version for the identification of the officer between Hitler and Jacob is Oberst Erich Kahsnitz. This photograph by Walter Frentz is famous for being the cover of 'Hitler's War' book by the author David Irving.
Source:
https://forum.axishistory.com/viewtopic.php?f=5&t=66810&p=605541&hilit=alfred+jacob#p605541