I'm stuck with this problem for several weeks now and will try to give a short and detailed explanation below:
Situation
Users visiting the websites and has the option to generate an image with the GD-library. So every users generated a personal image. Simple... until now. After generating the image, the user gets the option to share this image to Facebook. This is done via the OpenGraph protocol.
What's working (Yeah!)
Generating the image is working perfectly fine. Sharing something to Facebook is working also.
Problem
Although the following code is used on sharing the image (fbrefresh=CAN_BE_ANYTHING). FB stills pulls an old image. Sometimes this is a really old image, sometimes it's a more current generated image. But never the just generated image.
And now?
As said I've already tried the fbrefresh=CAN_BE_ANYTHING. Also in de debug tool the right image isn't showing up, but this is probably because the generated image has an unique ID generated from the users cookie. So this id is only usable when the users clicks on generate and after that shares the generated image.
Is there any example on the internet that uses the same sort of strategy and is working? I've searched half the internet and didn't found it yet it's becoming more and more frustrating.
After generating the image, the user gets the option to share this image to Facebook. This is done via the OpenGraph protocol.
What exactly do you mean by the latter? Are you just uploading that image to the user’s wall/one of their albums, or are you publishing an Open Graph object with a user-generated photo attached? (Btw., user-generated photo is meant literally for OG actions – you should only do it with photos that the user has taken using f.e. their mobile phone camera while they where undertaking the action. I doubt if a GDlib-generated image fits into that description.)
Although the following code is used on sharing the image (fbrefresh=CAN_BE_ANYTHING). FB stills pulls an old image.
And by “pull” you mean what exactly, again? Do you upload the photo as an HTTP POST upload, do you upload it by URL, did you specify it as og:image for an OG object, or do you pass it as user-generated photo while publishing an action?
Now, usually the easiest way for resources referenced by a URL to get properly refreshed by the requesting client, is to attach a different value to the query string/as a GET parameter – f.e. the current unix timestamp: …/image.php?1984372634 or …/image.php?foo=bar&forcerefresh=1984372634
Since this value changes every second, it makes each of those URLs a different URL, and the requesting client absolutely has no choice but to request that resource, because he can not have it in its cache already.