Example of fullscreen background images.

gistfile1.js

app.backstretchImgs = function() {

	$.each($('img.backstretch'), function() {

		var $img = $(this);
		// bind to resize
		$(window).bind('resize', function(event) {
		
			// remember to place into DOM first if you need access to width & height
			// access width & height with this.width and this.height
			var imgRatio = $img.width / $img.height,
				windowWidth = $(window).width(),
				windowHeight = $(window).height(),
				windowRatio = windowWidth / windowHeight;
	
			if ( imgRatio > 1 && windowRatio <= imgRatio)
			{
				var bgHeight = windowHeight,
					bgWidth = (imgRatio > 1 && windowRatio <= imgRatio) ? (windowHeight / $img.height) * $img.width : bgHeight * imgRatio,
					bgCSS = {
						'top' : 0,
						'left' : ((windowWidth - bgWidth) / 2)  + 'px'
					};
			} else {
				var bgWidth = windowWidth,
					bgHeight = (imgRatio > 1 && windowRatio >= imgRatio ) ? (bgWidth / $img.width) * $img.height : bgWidth / imgRatio,
					bgCSS = {
						'left' : 0,
						'top' : ((windowHeight - bgHeight) / 2)  + 'px'
					};
			}
			
			$img
				.width(bgWidth)
				.height(bgHeight)
				.css(bgCSS);
		});
	});
};