This set of posts comes from Pastor Mark Driscoll and his wife Grace. The sermon series The Peasant Princess brought up dozens of questions that they felt they should respond to. The result is this blog series: Christian Sex: Frank Answers to Honest Questions.
Answer: Nude images of your spouse are redeemed images and, providing your spouse is agreeable to this arrangement, you are free to operate by conscience. Practically, we would urge you to be extremely cautious to not allow any other people to see those photos in order to ensure protection of your marital privacy. Since the purpose of sexual activity is oneness, your option is both creative and permissible because you are being as intimate as you can be when distance separates you. However, if either of you has a history of pornography, or if either of you becomes dependent on the images to perform, then this might not be helpful for the marriage and building oneness.