You need to use the [IMG]-tag and need to insert the link to the image (usually obtained through some option through the context menu/right-clicking on the image - my browser gives me the option "Copy Image location", if yours doesn't feature one, it should feature something else to obtain it a bit more complicated (displaying image information, viewing the source code or viewing the image in a separate tab)).
So using [IMG]http://i53.photobucket.com/albums/g68/Cats_Are_Aliens/Banners/Bloodfeast_zps6d83e524.png[/IMG] in the editor will produce in the post.
EDIT: If you want to see how a person did post something, a handy trick is just to quote that post and remove the added [QUOTE]-tag - it will give you the original post and you can play with the used code [quotes get discarded from the quoted post, so you need to quote the original post if the interesting content is inside a quote]