I chose a background image for one slide, and then when I wanted to use it for another, I had to upload it all over again. How can I just re-use a background from somewhere else in the deck?
If you want to apply that image to all slides you can change the "master slide". If you just want to apply it to some of the slides, I think the easiest way is just to copy that slide with the image you wanted and paste it. The pasted slide will look exactly the same as the original. Then you can delete the content/change the layout etc., but the background image will still be there.