Prisons are not “torture,” in and of themselves. Society has a right to protect itself from criminals by segregating those criminals from the rest of society until such time as the debt has been paid or society deems that releasing an individual on parole is an acceptable risk. While you are free to your opinion that other means of punishment are more humane, keep in mind that accusing the greater portion of society who disagree with you of a crime as serious as torture, without just cause, is not a charitable or humane means of supporting your opinion.
That said, it may well be true that conditions within some prisons are in desperate need of reform. However terrible the crimes committed by the people confined to prisons, their safety is indeed a social responsibility and we should not merely shrug off reports of inhumane living conditions, gang activity, rape, beatings, and murder, with either a flippant or a bitter, “Well, he got what he deserved.” For Christ too was once a prisoner and listed prisoners among those with whom he identified when he said, “Truly, I say to you, as you did it to one of the least of these my brethren, you did it to me” (Matt. 25:40).