We're a website completely written in PHP, we use facebook metatags since we provide facebook sharing, liking, etc...
problem is when we share a link from our site to facebook, it shows the picture correctly, however trying to reshare the same link from another user, removes the picture and shows the link only.
Further troubleshooting using the FB debug tool shows below error message: Unable to download og:image: The image referenced by the url of og:image tag could not be downloaded.
The weird thing is that the image is already see and accessible in the debugger!!
A sample page: http://fbcomics.com/home/index/92/date/1462
Debugger for it: https://developers.facebook.com/tools/debug/og/object?q=http%3A%2F%2Ffbcomics.com%2Fhome%2Findex%2F92%2Fdate%2F1462
Your cooperation is highly appreciated.
I think that you probably need to urlencode() the url value going into the content attribute of your og:image meta tag.
This might be related to a recent Facebook bug. https://developers.facebook.com/bugs/239522122851150
Issue was solved by itself. It seems that Facebook needs sometime (weeks I think) to store the page information including the picture using its crawlers.
If you face this, most probably you'll need to wait for sometime before sharing your new pages.
Thanks,