I'm working on a project involving Gallery 3, and one of my goals was tight Facebook integration. Today I've wanted to make sure that when someone shares a page from my gallery on Facebook, it'll show up OK.
After some digging around I found some interesting stuff:

Facebook's URL Linter

Whenever you want to test / troubleshoot your shared URLs, use this tool to see what Facebook makes of it. It'll take a url and display all metadata that Facebook harvests from the page, like its title, description and thumbnail.

Metadata tags

Page metadata can be "force-fed" to Facebook using <Metadata> tags.
I haven't been able to find a complete list, but these folks will do for most people:

  • title
  • description
  • image_src

Open Graph Tags

If your page represents a real-life object (such as a celebrity, movie, restaurant) you might prefer using Open Graph. Don't be misled by the name, this standard was created for Facebook. It's not some internet-wide phenomenon (at least for now!)

These resources should be enough for you to be able to make your page Facebook-shareable.