If you want to directly attach a photo to the site you need to be a subscriber for that feature (it's $25/year) and you can access that information through your User CP at the top of the page.
If you just want to link an image this should help you Linking Images
You don't have to subscribe to have your picture appear in the post.
You can hot-link to an image from any service (like imageshack or photobucket that allows hot-linking)