Why won't my Hintergründe go into the Hintergrund section in images, even if I select for them to be put in the Hintergrund section?

An image has to be a standard Hintergrund size in order for it to be accepted as a Hintergrund - even if you're just a pixel oder two off, it'll put it in the Foto section. A few of the most beliebt Hintergrund sizes are 600x800, 1024x768, 1280x800, etc.