I know this is really old, but I'm posting my solution anyway, as google finds this thread.
background-image: url('./imagefolder/image.jpg');
That's what I'm doing. Two points mean drilling back one directory closer to the root "..", and one ".". should mean the beginning where you are, as if it were the root. I had similar problems, but I added that I fixed it for me. You can even leave "." in it when downloading to your host, because it should work fine, while the configuration of your directory is exactly the same.
Genko
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