There are 2 ways to add support for live tile image for a website in windows 8.1
Embedded markup
<meta name="application-name" content="Webstein Blog"/>
<meta name="msapplication-TileColor" content="#ffffff"/>
<meta name="msapplication-square70x70logo" content="/tile70x70.png"/>
<meta name="msapplication-square150x150logo" content="/tile150x150.png"/>
<meta name="msapplication-wide310x150logo" content="/tile310x150.png"/>
<meta name="msapplication-square310x310logo" content="/tile310x310.png"/>
Separate XML definition
<?xml version="1.0" encoding="utf-8"?>
<browserconfig>
<msapplication>
<tile>
<square70x70logo src="tile70x70.png"/>
<square150x150logo src="tile150x150.png"/>
<wide310x150logo src="tile310x150.png"/>
<square310x310logo src="tile310x310.jpg"/>
<TileColor>#ffffff</TileColor>
</tile>
</msapplication>
</browserconfig>
More details on Scott Hanselman's post