I'm spending some time in the Apple iTunes store. Release Me at $8.99 is pricey but ultimately can save you money or time spent in a court room. The ability to get a photo and a signature at the same time is amazing.
This is a video from the vendor web site:
Basically, the application allows you create a photo enhanced model release that can create a signed Adobe pdf copy. You can print or e-mail a copy to the model, publisher or whoever needs proof of permission.
If you plan to record folks and use their image for public display or for profit you need a release, paper or electronic. This is a good option. This is an excellent idea and it is a investment that can save you hassles later.