How Does The Facebook 'share' Button On Stack Overflow Work?

I am looking to add social icons to our site, giving customers the ability to 'like', tweet and share content on their facebook and twitter profiles. I have noticed to the left of

Solution 1:

When you click on the share button, you call a script on facebook.com that will then in turn access the page pointed to in the querystring (?u=xxxxxx).

Facebook will parse that page and grab the first few images it finds, a description and title from the page. That is what it shows to you and allows you to add some additional text (as well as edit the title/description/and choose different images).

If that page contains the specific meta tags that facebook asks you to add to the page, then they'll use those to populate the title/description/image. This allows the webpage author to control how their page shows up in a facebook feed (although the user could still edit it before posting). These meta tags would need to be in that particular page to be used by facebook.

If facebook cannot access the page because it's password protected, etc. - then it cannot parse the meta tags and will then just show the user the URL as the title with no description and thumbnail.