How long is Facebook caching the sharing thumbnails? I've added a custom thumbnail for my page using:
<meta property="og:image" content="/path/to/my/image" />
But on pages my previous image is displayed => it is cached somewhere on FB servers.
Any ideas how to flush that cache or how long does it take once FB loads a new image?
Check the page with Facebook URL Linter, it seems to reload the thumbnails images in the cache.
Facebook images are cached on a different servers on a different location. According to what I have read, it will take 3 to 5 years before the image is refresh/deleted permanently after the last time it was accessed. So if the image keeps being accessed it won't be flushed. Not until you give up on shutting down your site.
FYI the FB linter link above doesn't work anymore. This seems to do the trick though:
来源：https://stackoverflow.com/questions/3845095/how-long-is-facebook-caching-the-sharing-thumbnails