Can you explain the story behind Baba's portrait that Kakasaheb Dixit received before his trip to Shirdi?

Certainly. The portrait of Sai Baba played a significant role in the events described in chapter 51. This specific photograph was one that Baba's devotee, Megha, used to worship with great devotion. The glass on the portrait had broken, so it was sent from Shirdi with Balasaheb to Nagar for repairs. After being fixed, the portrait was kept covered in Balasaheb Mirikar’s drawing room. It was as if it was waiting for Kakasaheb Dixit's arrival. Balasaheb entrusted the portrait to Madhavrao Deshpande, who then unveiled it and gave it to Dixit. This was so Dixit could feel he was traveling "in Baba's company." The sudden appearance of this holy image, which he had longed to see, overwhelmed Dixit with joy.