According to this page: https://developers.facebook.com/docs/plugins/share-button, normally, Facebook only scrapes your site for Open Graph information once a day. You need to manually go to the Facebook Debugger Tool https://developers.facebook.com/tools/debug/ and paste your URL into the box and click on the
Debug button and then on the
Fetch new scrape information button each time you update your page's Open Graph information to see the updates in the Facebook sharer page once you update your HTML.
There is also one particular Facebook scraper bug to watch out for. Sometimes, even when the Open Graph Image and related information specified in the head section of an HTML page is correct, upon hitting the
Fetch new scrape information you may get the following error message:
og:image could not be downloaded or is too small
If your image fits the Facebook guidelines and you're still getting this message, then just hit the
Fetch new scrape information button a few more times and it will go away (or, even if it does not, you can safely ignore the message).
Also, when embedding your Facebook sharing URL inside HTML, remember to URL-encode it. For your example, the HTML should be something like:
<img src="share-button.png" alt="Share on Facebook" />
If after doing these things, the sharing feature still won't work, then paste the following link in the Facebook Debugger Tool (with the
fbrefresh=CAN_BE_ANYTHING query string field) and click on the Debug button to clear the cache, then paste http://www.example.com/ into the field to reload the OG data into the Facebook servers: