im1 = new Image(675, 485);
im1.src = '/img/upload/01.jpg';

im2 = new Image(675, 485);
im2.src = '/img/upload/02.jpg';

im3 = new Image(675, 485);
im3.src = '/img/upload/03.jpg';

var image1 = 1;
var image2 = 2;
var frame = -50;

function animation()
{

    if ((frame >=0) && (frame < 51)) {
        var el = 'img' + image1;
        $(el).style.zIndex = 88;
        $(el).style.display = 'block';    
        $(el).style.opacity = 1 - (frame * (50) / 2500);
    
        var el = 'img' + image2;
        $(el).style.zIndex = 92;
        $(el).style.display = 'block';    
        $(el).style.opacity = 1 - (1 - frame * (50) / 2500);
    }

    frame++;
    
    if (frame == 150) {
        image1++;
        if (image1 == 4) {
            image1 = 1;
        }
        image2++;
        if (image2 == 4) {
            image2 = 1;
        }
        frame = 0;
    }
}