HTML set image on browser tab [duplicate]
It's called a Favicon, have a read.
<link rel="shortcut icon" href="http://www.example.com/myicon.ico"/>
You can use this neat tool to generate cross-browser compatible Favicons.
<link rel="SHORTCUT ICON" href="favicon.ico" type="image/x-icon" />
<link rel="ICON" href="favicon.ico" type="image/ico" />
Excellent tool for cross-browser favicon - http://www.convertico.com/