Is the person you are dealing with willing to let you take a picture of their drivers license? I would have no issue, if I was selling a big ticket item.
I wouldn't let that happen, copies of your ID shouldnt be floating around for others to have. If a buyer wants a bill of sale, wants proof of who I am I would show my ID but no copy on paper or digits will be going anywhere. Buyer can use whatever means he wants to check on the item, VIN check etc, if the item requires a title obviously that will be produced as well.