A model release is basically a declaration by the model that he or she has assigned all rights to the images to the photographer to use as they see fit. It should be signed and dated by the model and a witness, who cannot be the photographer. If the model is under 18, a parent or guardian must sign on their behalf. Printing one or two small examples of images from the shoot on to the form can also help identify the images at a later date.
A simple release
should read something along the lines of 'I hereby give permission
to [photographer's name] to use my photographic likeness in all
forms and media for advertising, trade and any other lawful purposes'
In reality, model releases are never this clear-cut. In this day and age, with concerns over privacy, it is best to be concise. For this reason most model releases are more specific as regards the intended use(s) of the photograph. It is common to see lines that state the images may be used for any purpose except for those that may be defamatory or pornographic or imply certain medical conditions. If the model has a specific request for the photos not to be used for a certain purpose then this also may be written into the release.
If you are planning on taking images to be used for a stock library, most will have their own forms available for download. As with anything of this nature, if you decide to draw-up your own model release form it is important to have it checked by a legal professional