In what situations do i need a property release for a photograph taken by me, uploaded to my website? Is it if the photo generates revenue?

There are potentially a number of copyright issues in a photograph, even one taken by you. You have to look at what is contained in the photograph and see if you are copying something that itself is protected by copyright. This can range from sculptures to paintings to even buildings, if those buildings are on private property and not viewable from a publicly accessible area and were built after a certain date. Copyright is not your only consideration. You also need to check for trademarks and for the rights of privacy of persons who are in your photograph. For trademarks, you cannot use someone else's trademark in a way that makes it appear that they are associated with or endorse you or your product without their permission. People have similar rights to keep their images from being used without permission to endorse someone's product or service. In general, the commercial nature of your intended use makes it more important to clear everything before using the photograph to generate revenue, In certain instances, private uses may be protected but a commercial use tips the scales in many cases to impermissible use.