How Does Facebook Know What Image To Parse Out of An Article?

Question

First off I want to say that I wasn't really sure where to post this but it is very much programming related. If it is in the wrong spot I apologize and please let me know where I should post it instead.

When sharing an article on a friends wall, facebook will grab a thumbnail of the article. How do they always get the right thumbnail from articles?

It doesn't grab the logo img element of of http://www.nytimes.com/2010/06/07/world/asia/07convoys.html?hp for example but rather grabs the correct image element that corresponds with the article.

I'm looking to do something similar and was wondering of a good way to parse the html to find the image given this example. Thanks.

Answer 1

Actually, Facebook's way of finding thumbnails isn't so magical. It searches for a set of <meta> and <link> tags which specify which title, description, and image to use.

If it cannot find any of the <meta> and <link> tags it is looking for, it basically asks the user to choose whichever <img> tag fits.

In the case of the NY Times, it uses the following:

<meta name="thumbnail" content="whatever.jpg" /> 

Facebook recommends you use a <link> tag instead for the thumbnail.

<meta name="title" content="title" /> <meta name="description" content="description " /> <link rel="image_src" href="thumbnail_image" /> 

Source: Facebok Share/Specifying Meta Tags