Conversation so far:
Who took the famous photo of Y.A. Tittle?
Morris Berman of the Pittsburgh Post-Gazette took the famous photo
When was the famous photo of Y.A. Tittle taken?
The photo was taken on September 20, 1964
What was the famous photo of Y.A. Tittle of?
The photo was of Y.A. Tittle

Question: What was he doing in the picture?
Self-contained rewrite: What was Y.A. Tittle doing in the famous picture?