In a pre-trial hearing in Los Angeles Superior Court, Alameda County Prosecutor David Stein said he plans to use the photo as evidence that Mehserle knew the difference between his Taser and his gun, just before he shot and killed Grant.
Defense attorney Michael Rains plans to argue Mehserle mistook his gun for his Taser.
Grant's family said the picture proves that Mehserle knew the difference between his Taser and his gun.
"How can you deny the truth, I mean Oscar took a picture of Johannes Mehserle moments before he was killed," Grant's friend Jack Bryson said.
According to Stein, Mehserle drew his Taser on grant and reholstered it. Then a few minutes later, Mehserle pulled his gun and fired into Grant's back, as the 22-year-old lay face down on a platform.
"Oscar was a United States citizen, he didn't deserve what happened to him. There was no reason for any of these cops to use Tasers, anything like that," Grant's aunt Zeporia Smith said.
On Tuesday, a jury of eight women and four men was selected to decide if Mehserle is guilty of murder. Grant's family and friends were disappointed the panel includes no African Americans.
"It seems like Oscar Grant and his friends are on trial. Will he get a fair trial? No," Grant's friend Tracie Cooper said.
"Typically in Los Angeles, you would expect to see at least two or three African Americans on such a jury. If I were the prosecutor, I would be disappointed, I would be somewhat concerned. But it's still possible depending who these people are, that they will deliver the right verdict after they've heard all the evidence," jury consultant Paulette Taylor said.
In other rulings, Judge Robert Perry decided prosecutors can introduce evidence of a racial slur used by both Grant and BART officer Anthony Pirone just before the shooting. And, Judge Perry will allow Grant's girlfriend to testify about what happened the night of the shooting, including a cell phone call she received from Grant, just before he was shot.
"You have a gun, you have a racial word and then you have someone that was killed," Bryson said.
Opening statements begin at 8:30 a.m. and Grant's family and friends plan to be there in force. It's uncertain whether there will be any Mehserle family or supporters inside the courtroom.
The video and Grant's own photo will likely be the centerpieces of the trial.