You can access the release of information form here. Clients can fill it out, scan it, and send it back to you via email. They can also print it, fill it out, take a picture of it, and send the picture to you. If they are unable to do either of these things, you can have them reply to the release you send them saying, "I, [NAME] have read the release of information document provided and consent to all its stipulations."
NOTE: You do NOT need a release form if you do not have a photo and if there is no personally identifiable information in the materials you provide.