Last modified: 2014-02-14 13:20:47 UTC
e.g. When shared on facebook http://www.wikidata.org/wiki/Q6294 would provide the image http://commons.wikimedia.org/wiki/File:Hillary_Clinton_official_Secretary_of_State_portrait_crop.jpg to facebook as a preview due to it being linked from the image property in wikidata https://developers.facebook.com/docs/opengraph/howtos/maximizing-distribution-media-content/#tags
Equivalent data for G+ may be slightly different http://webmasters.stackexchange.com/questions/25581/how-does-google-plus-select-an-image-from-a-shared-link
More data on Google's rich snippets and preparing structured data for search results http://support.google.com/webmasters/bin/answer.py?hl=en&answer=99170
Documation for Twitter Cards https://dev.twitter.com/docs/cards Photo, Large Image, or Summary card type might be appropriate for wikidata links
How does this differ from bug 31338?