Can you explain the history of the Sai Baba portrait that was given to Kakasaheb Dixit before his trip to Shirdi?

Certainly. Chapter 51 details the origin of this specific portrait. It was a photograph of Sai Baba that was ardently worshipped by Megha, a devoted disciple, who regarded it as Lord Shankar himself. Unfortunately, the glass on the portrait had broken, so it was sent from Shirdi to Nagar for repairs. It was brought to Nagar by Balasaheb. After being repaired, the portrait was kept covered with a cloth in Kakasaheb Mirikar’s drawing room. It was as if it was waiting specifically for Dixit's arrival, and Balasaheb entrusted it to Madhavrao, who then presented it to Dixit before their journey.