Releases
A release is a written agreement between you and the person you are photographing, or the person who owns the property you are photographing, which gives you permission to sell the image commercially. If the image is used in an advertisment or promotion it will need a release, but you can sell an image for Editorial use even if it doesnt have a release.
Commercial use
is when an image is used to advertise, promote, sell or endorse a product, service, organisation or brand. Examples include billboards and print advertising.
Editorial use
is when an image is used in conjunction with, and to illustrate, a story or descriptive piece of text. Examples include magazine or newspaper features and books.
A model release
says the person being photographed has given consent to be photographed and to the use of the images you capture. It doesnt just apply to professional models or situations where people know they are posing for photos. You should seek to get a signed model release any time that your photos contain images of people, unless you are certain that you will never want to use them for anything other than editorial purposes.
A property release
says that the owner of a certain property, such as a pet or a building, has given you consent to take and use images of the property. You dont need one for public property, such as government buildings (although you may run into problems just from photographing them, for security reasons). But for images of private property and particularly of objects that are closely identified with specific people you are safer if you get a release.
The releases you obtain should be saved forever and should be linked in some way with the photographs to which they relate. You can expect to be asked to produce them whenever you license an image, and you will need them if you ever have to defend yourself in court.
Some definitions courtesy of American Society of Media Photographers.
Why you need releases for people and property
To maximise the potential to sell your images for Commercial use.
To sell your images Royalty Free.
If a person can recognise themselves in an image. Examples when you need a model release also include, crowd scenes, team sports, and scenarios when the face is not visible such as parts of the body, or silhouettes. For a picture of two people shaking hands, where only the hands are in shot, you need two model releases.
Remember, if you dont have a release for certain content, you can sell it as Rights Managed (RM) and set restrictions to Editorial use only.