Go to the courthouse where you had your trial or where you had your mug shots taken.
Ask the clerk for a copy of your mug shot. More than likely you will be asked why you want a copy and who you are in relation to the person in the shot. If you are the individual or a family member (or the individual's lawyer), say so and indicate that it is for personal records. You can not actually use the mug shot for anything. If you are a member of the press your county may not allow you to obtain the mug shot.
Pay the processing fee for the mug shot. Once you have paid for the picture, the clerk makes a photocopy of your mug shot and gives it to you.