Suppose I serve an image and if someone visits from a forum then I want it to download that image. If they visit again from the same forum then I want it to use cache, but if they visit from another forum and reference that same image I want it go ahead and re download that image. Is that possible?
The proper way to do this is to use the HTTP
Note that you can't actually tell the browser to automatically use the cached copy for all requests from the "same forum", for two reasons: first, the browser has no idea what constitutes a "forum", and second, even if you defined "same forum" as, say, "same domain", the