Chief prosecutor Gerrie Nel took an aggressive stance with Pistorius on the stand for the first day of cross-examination, telling the 27-year-old to "take responsibility" for fatally shooting Steenkamp.
Nel said Steenkamp's head "exploded" when it was struck by one of the four hollow-point bullets Pistorius fired through a closed bathroom door.
The photo showed a side view of Steenkamp's head "with a mass of blood and human tissue on the back and upper parts," according to the AP report.
''It's time that you look at it,'' Nel told Pistorius.
''I remember,'' Pistorius said, becoming distraught and turning away from where the photo was shown on a TV screen next to him. ''I will not look at a picture where I'm tormented by what I saw and felt that night. As I picked Reeva up, my fingers touched her head. I remember. I don't have to look at a picture, I was there.''
Pistorius added that Steenkamp died in his arms before paramedics arrived.
''I made a mistake,'' Pistorius said.
''What was your mistake?'' Nel reportedly shot back.
Pistorius said he ''took Reeva's life.''
''You killed her,'' Nel said. ''You shot and killed her,'' and he asked Pistorius to say it. Pistorius would not, saying merely: ''I did.''