I have always used the image tag to post a photo referencing a site like Photobucket, Example:
To show this picture of the lovely weather at the top of Tuckernam's Ravine last Saturday, you would include the URL pointing to the photo between two IMG tags in brackets. I'm not sure how to "show" it without having the picture show up, so I'll use { instead of [, hope that makes sense
{IMG]
http://i174.photobucket.com/albums/w111/Be_Prepared/FH000010.jpg[/IMG}
(If you change the open { with [ and close } with ] you get: