That is absolutely right. I think that US Paper money is pretty tricky for me to add, though not impossible. Most other World Paper Money is somewhat predictable. But, I do have a bit of a personal rule: no image, no addition to the database. As I am constantly adding code, images, and sales histories to the site (on top of my other two actual jobs) I don't personally go out of my way to research banknotes that are not listed on the site, but the process can definitely be aided by you guys.
On a related note: the images you send do not have to be scans of your actual note. Just find some images on eBay that are the same as the one you wish to add, and you can skip the whole scanning stage.