$('.projectHolder').hover(

        function() { //This is the hover in function

            $("img", this).stop(); //Stops any animation being done on the button

            $("img", this).css({opacity:1}); //Changes the opacity back to not if not already

            $("img", this).animate({opacity:0.5},400); //Now animates the opacity to the user defined value          

        },

        function() { //This is the hover out function

            $("img", this).animate({opacity:1},400); //Animates the opacity back to 1

        }

)

jQuery Fade/Animate an image in a class

class, image, jquery

jQuery