How to attach a site thumbnail from user submitted links in a facebook application

The Facebook application I had in mind has users submit links from sites. I would like there to be a thumbnail of the site, similar to what happens when you post/message someone a link and a thumbnail automatically shows up. 开发者_开发技巧Any thoughts on how to go about doing this?

The sites you link to need to have Open Graph tags (https://developers.facebook.com/docs/opengraph/) on their pages to set the default image, description and title for this to happen. If those meta tags are not set, the first image on the page will be the default along with other generic information Facebook is able to scrape from the page.

If you want to test out a few pages and see what information they have set, use Facebook's URL lint tool (https://developers.facebook.com/tools/debug). Simply copy and paste any URL in there.