var LOGO_PATHS = new Array(
    "pics/logo_burning_letters.png",
    "pics/logo_burning_glow.png",
    "pics/logo_glow.png",
    "pics/logo_ice.png"
);

function changeLogo() {
    var newLogo = randomNumber(0, LOGO_PATHS.length - 1);
    document.getElementById("logo").src = LOGO_PATHS[newLogo];
}

function randomNumber(min, max) {
    var r = Math.random();
    r *= (max - min + 1);
    r += min;

    return Math.floor(r);
}