As Echoes said, upload the photo to any image sharing website and paste the Direct link into a thread and it will appear. As well as ImageShack, you could use
tinypic or
photobucket.
For example, with tinypic once you have uploaded an image, you will have a screen similar the one in the spoiler. You want to copy the link in the red box (the Direct Link) into the thread.
SPOILER: Click to view
Posted on Saturday, 28th January 2012