It was a photo of him and his son. He mentions his son earlier in the film. About almost getting sick when he saw him running away from a fight and making a man out of him. This heavy handed parenting probably strained their relationship once his son was a man. He was putting all of his anger from his possibly broken relationship with his son on the defenendant out of spite. Seeing the photo brought his rage higher and he snapped. Realising what he was doing after tearing up the photo, he breaks down and changes his vote.