Edit in JSFiddle

<div class="cover_pan"><img src="https://lh3.googleusercontent.com/-0ACeL28sLVc/UM2_vAcNuOI/AAAAAAAAB0o/9LmipWC66uI/s800/404.png"></div>

.cover_pan{
    background: #fff url(http://placehold.it/800x287&text=Oops!%20Page%20Not%20Fond) repeat 800px bottom;
    height: 287px;
    margin-left:1px; 
    overflow: hidden;
    position: relative;
    width:800px;
    margin:0 auto;
    -moz-animation-name: pan;
    -moz-animation-duration:40s;
    -moz-animation-iteration-count: infinite;
    -moz-animation-timing-function: linear;
    
    -webkit-animation-name: pan;
    -webkit-animation-duration:40s;
    -webkit-animation-iteration-count: infinite;
    -webkit-animation-timing-function: linear;
}


@-moz-keyframes pan {
    0% {
        background-position: 1338px bottom;
    }
    100% {
        background-position: left bottom;
    }
}

@-webkit-keyframes pan {
    0% {
        background-position: 1338px bottom;
    }
    100% {
        background-position: left bottom;
    }
}