Quick function to check viewport size and chop/crop images (CSS3) for mobile views.

octopress.js

var bt = {}; // to call the functions outside of the jQuery wrapper because OctoPress is a bit of a JS mess. Hey, that rhymes.

(function($){
	bt = {
		checkWinWidth: function() {
			var width = $(window).width();
			if (width <= 500) {
				if (!$('body').hasClass('mobile')) {
					$('img').each(function(){
						var $this = $(this);
						$this.replaceWith($('<div class="blowup" style="background-image:url(' + $this.attr('src') + '); background-size: cover; background-position:50% 50%;background-repeat:no-repeat;height:200px;width:100%;" /></div>').data('orig',$this));
					});
					$('body').addClass('mobile');
				}
			} else {
				if ($('body').hasClass('mobile')) {
					$('div.blowup').each(function(){
						var $this = $(this);
						$this.replaceWith($this.data('orig'));
					});
					$('body').removeClass('mobile');
				}
			}
		}
	};

	$(window).resize(function(){
		bt.checkWinWidth();
	});
})(jQuery);