ejb.github.io > brief notes & experiments by @elliot bentley

Dynamic promo image meta tags in Labour's 'voting record' app

I noticed a link on Facebook today to web app from the Labour Party which dishes up unflattering information about your nearest Tory or Lib Dem MP. Aside from the data capture / propaganda aspect, it’s intriguing because of the customised promo image that appears when you share your result.

Screenshot of Facebook post with customised promo image

Without any extra URL parameters, the page has a generic promo image. When the URL has an extra string on the end, eg graphic/tory-against-01vat-02tuit-03nhs-04bed-11nmw-12jobs-13ener-14sure-15gps.png/, the page then has a special promo image as specified by the URL. The page contents appear the same to the user, but the images that appear on Facebook and Twitter are customised.

The server-side code, if written in PHP, presumably works something like this:

<?php
$url = $_SERVER['REQUEST_URI'];
$url_components = explode( 'graphic/', $url );
if ($url_components[1]) {
    $image_url = 'http://storage.googleapis.com/voting-record/'+$url_components[0];
} else {
    $image_url = 'http://action.labour.org.uk/page/-/Images/votingrecordgeneric.png';
}
?>
<meta property="og:image" content="<?php echo($image_url); ?>">

Indeed, if we try to load up the page http://www.labour.org.uk/w/tory-libdem-voting-record/graphic/blah-blah-blah.png/, the meta image URL becomes http://storage.googleapis.com/voting-record/blah-blah-blah.png (a 404).

It’s a simple approach, but one I might try for myself in future interactives with a ‘customised result’ aspect. Could also be useful for A/B testing.

Posted 30 Mar 2015