I’m toying with building a small library that will take a URL, load and parse it (using Mechanize and Loofah), and spit out a title, description/summary, and the ‘main’ image. Sometimes it’s a piece of cake, like when they have Open Graph tags indicating all of that information in the headers. (I also plan to work on oEmbed support.)

But it’s a huge headache, because there are myriad standards, with most people not bothering to follow any of them. I’ve learned about all sorts of declaring “the image” for a page, like og:image or a rel=”image_src” link, but most of the time I have to try to parse all the tags and find the biggest. But that’s really error-prone, because lots of people don’t bother setting height and width parameters on their images, so I end up picking a 16×16-pixel icon as the “biggest”. (I categorically refuse to actually download every image to extract its dimensions for this. It’s a huge waste of bandwidth.) On Lifehacker, my code typically returns a banner image as the largest image.

And when an og:image is defined in the headers, all bets are off for what it is. Maybe it’s the largest image on the page — yay! Maybe it’s a 64×64-pixel thumbnail. (Boo!) Or maybe it’s the site’s logo. It might be an absolute path, but it might be relative, in which case I have to construct a new URL to it based on what I think the site’s domain is after account for having followed redirects.

And then there’s just insane stuff. If no og:title is set, I try to get the