In working through the backgrounds, ran across this question.
When evaluating the response from the GET /v3/me/backgrounds, see that there is a section for a custom name, and an array of images (with image sizes).
When posting, only parameter listed is the image file.
When creating background images, are we limited to a single image (and not being able to specify which image size), defining the name of the image background?
One side note about the GET as well, it only returns the 4 preset background, and does not return any previously uploaded files.