To set the image as background, right click the image and choose 'Set as Background'

<a href="http://www.funmunch.com.com" target="_blank"><img src="http://www.funmunch.com/events/patricks/st_patricks_day_graphics/st_patricks_day_cliparts/st_patricks_day_clipart_6.gif" alt="St.Patricks Day Cliparts" border="0"></a>