$(function(){
imageOver();
})
function imageOver() {
$("img.over").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}
);
});
}