Tough to say, something tells me though that you used the term "revised the image". Did you ever upload the original, and did that one go thru? Are you your uploading the jpg or png, not a psd or something. Also, maybe if it is a revision try changing the name, to Image2.jpg or something, just in case there's a cache issue. Things like that, otherwise just move all your files except that image into a new folder, then create and save that image there again. Or something like that, just brainstorming until you get it thru.
I have had times when setting up a channel where it gets stuck in kind of a cached status. It's like no matter what you do it doesn't take any changes. What I have done is to use a new json file for the URL , force it to accept that one, then change it back to the one that you are making changes on.
I know it sounds like a long way around it, but sometimes by making a drastic change when you go back to what should work it does.