Uhhh... yeah. I'm kind of new to this too, and the only way to put it as a skin, I believe is to put the picture under 'Installable journal skins' or something like that. Because i've been browsing under this category and it had a button on a button that said 'install into journal'
So that's what I'm tryna do now, so you can use it. But the thing is, I have no idea what I'm doing!!