Favicon

Favicon
Favicon - Wikipedia
 * "A favicon (short for favorites icon), also known as a website icon, shortcut icon, url icon, or bookmark icon is a 16×16, 32×32 or 64×64 pixel square icon associated with a particular website or webpage. A web designer can create such an icon and install it into a website (or webpage) by several means, and most graphical web browsers will then make use of it. Browsers that provide favicon support typically display a page's favicon in the browser's address bar and next to the page's name in a list of bookmarks. Browsers that support a tabbed document interface typically show a page's favicon next to the page's title on the tab."

HTML5: 

HTML:   

Internet Explorer has a slightly different format:   

http://favicon-generator.org/ says to use:  

Generator
favicon.ico Generator

Converter
ConvertICO.com - Convert .PNG format files to .ICO or .ICO format files to .PNG : Windows 7 compatible icons - http://www.convertico.com/