In truth, I actually didn't know how to do it. On the other hand, it isn't realy that obvious with the WYSIWYG format.
Spoilers are simple it's Code: [spoiler]Spoiler Text Here[/spoiler] as for whether a button might one day be added to the editor, perhaps but it's surprisingly complicated & I am notoriously lazy.
Code: [spoiler="Name goes here, subtitle/underside goes here"][/spoiler] I don't know why you're so interested in using graphic images though.