This photo (the only one I know of where He is holding prayer beads) appeared in Star of the West, Vol. 10, No. 9; August 20, 1919.
Below the photo are captions in Persian, as well as this in English:
"His Holiness Abdul Baha Abbas"
(possibly His English signature) and,
"This blessed picture was taken in New York City, December 2nd, 1912, Copyright by Jacob Schloss, New York, N.Y."
Mahmud's Diary does not mention a trip to a photographer's studio on this day, so this portrait may have been taken in His residence. That day He spoke on the meaning of "defending the rights of Baha'u'llah." He left America on the 5th of December.
After the war, Shoghi Effendi came to work as His secretary. In his first communication with Star of the West, a diary of his activities, the future Guardian included a response -- almost certainly to this photograph, published recently in the Star of the West -- by a believer, introducing it in these words, " (A) detailed supplication from Juanita Storch, exquisitely written, reveals the sentiments of love and of thankfulness. I have already quoted a few of her characteristic lines and I cannot prevent myself from sharing with you some of its charming passages;" here is what she says about the picture.
"A picture of the Master comes to me as he holds his rosary in hand outstretched to all who heed to this heavenly call. A picture of the Master comes to me as he holds his rosary, thinking of friends both far and near as pearls of his heart. A picture of the Master comes to me as he holds his rosary, chanting in a prayerful hour, ‘Glory to the Most Great Power.'“
Shoghi then added, "To this profusion of genuine sentiments and to this authoress of tender feelings, Abdu’l-Baha not only spends the days in revealing his words of appreciation, but even until late at night, when everything is hushed in silence and every tongue is at rest, then does the wakeful Beloved reveal his soothing words and his precious lines." (SW v. 10, p. 219)