I really debated whether or not I should chime in on this, as it could open a whole host of canned worms. Talking about what is and isn't original has lead to so many arguments in the past, and hurt feelings as well. But...
DJ Mighty- The problem with going that route, is that it's hard to call the end result original when it's using another person's pre-existing photos and such as its base. Even when you add layer upon layer of effects, filters, lines, shading and such, it's still really just a tweaked version of what someone else made.
I believe by "original", bonzai! means work you made from scratch on your own, without recreating what others have already done (be it in drawings, photos, paintings, etc.). Images like the one you and Cottus&Gyes made, while nice, don't really fall into the realm of original work. Not because effort wasn't put into it, but because of the source of the images within them.
If you both drew up your own takes on those characters in your compositions, then it could be considered original fan art, as it would no longer involve drawn over or filtered movie posters, screen grabs, and the like. But as it is, I don't think they can be called original works.
They're kind of like remixes in a way. You take a source tune, and reinterpret it. The end result is a remix, and not an original song. Well, that's more or less what you guys did, just in a visual fashion rather than an aural one