Original article

The HTML

<h1 class="bgClip">Clip Text</h1>

The CSS

.bgClip {
    background:url('../images/clouds.jpg');
    background-repeat:repeat-x;
    background-position:0 0;
    font-size:200px;
    text-transform:uppercase;
    text-align:center;
    font-family:'Luckiest Guy';
    color:transparent;
    -webkit-font-smoothing:antialiased;
    -webkit-background-clip:text;
    -moz-background-clip:text;
    background-clip:text;
    -webkit-text-fill-color:transparent;
    margin:0;

If you want to animate it

-webkit-animation:BackgroundAnimated 15s linear infinite;
    -moz-animation:BackgroundAnimated 15s linear infinite;
    -ms-animation:BackgroundAnimated 15s linear infinite;
    -o-animation:BackgroundAnimated 15s linear infinite;
    animation:BackgroundAnimated 15s linear infinite;
}
    @keyframes BackgroundAnimated {
    from {
        background-position:0 0
    }
    to {
        background-position:100% 0
    }
}
    @-webkit-keyframes BackgroundAnimated {
    from {
        background-position:0 0
    }
    to {
        background-position:100% 0
    }
}
    @-ms-keyframes BackgroundAnimated {<     from {
        background-position:0 0
    }
    to {
        background-position:100% 0
    }
}
    @-moz-keyframes BackgroundAnimated {
    from {
        background-position:0 0
    }
    to {
        background-position:100% 0
    }
}