You can upload two files, one for the custom thumbnail and one for the picture.
BUT on inkbunny, users can optionally disable custom thumbnails. So if you want be sure those floofs don't see the picture (like for April Fools day or something), you'll need a 2-page post with the thumbnail as page 1 and the full pic as page 2.
You can upload two files, one for the custom thumbnail and one for the picture. BUT on inkbunny, us