A couple of friends and neighbors recently got married. At least in my area and for the price/quality range of photographers they hired, they all received a CD containing decent quality jpegs as part of their package. With recent abundant availability of scanners and printers, you may be fighting a losing battle trying to protect your proofs.... Even if you say NO, many are going to do so anyway. Unless good size watermark goes across face or something (which I think, destroys the beautiful proof and defeats the purpose.....) I don't think there is much you can do about it...