$(function(){
	imageOver();
})
 
function imageOver() {
	$("img.ov").each(function() {
		var image = this.src;
		var extension = image.substr(image.lastIndexOf("."), image.length-1);
		var image_over = image.replace(extension, "_o"+extension);
 
new Image().src = image_over;
 
		$(this).hover(
			function(){this.src = image_over},
			function(){this.src = image}
		);
	});
}