So, you've just made that cool back end database with uploading image support, yet, when the user uploads a new image it isn't shown unless its a full refresh (shift-refresh). Well, I've solved the problem. No, you do not have to set annoying cache headers or any of that other nonsense. The fix is quite easy.
Let's say you have an image:
This will be cached on some browsers no matter how many headers you throw at it. So far, this has worked like a charm for me: