After the release of Barracuda Opera uses the <link rel=”icon”> or <link rel="apple-touch-icon"> meta in the site's header to find the logo, but it will only show in Opera if the attached image is wider than 114px.

<link rel="apple-touch-icon" href="http://youriste.com/images/apple-touch-icon.png">

Which should link to a 158px x 158px or larger image.

Without this, Opera Speed Dial icons will usually also discover and make available to you the OG image if a website has one declared.