Can't choose image I already have in folder

It would be brilliant if I could use an image that is already in a wp folder as the background image for a particular post. I sort of don’t want to upload 10 copies of the same image, just because that image works for 10 different posts.
Thanks! ??

Other than that, plugin works well, image actually shows up, and if it doesn’t show up, then just edit the post and choose a different starting point (right in my case). I did try another plugin, but didn’t get that one working. Thankful for this one.