Efecto nieve con cualquier imagen

Con este truco podés hacer que caigan por la pantalla varias veces la misma imagen con un efecto estilo nieve.
Puedes cambiar la imagen reemplazando por una tuya alojada en el servidor poniendo su nombre donde está en rojo.

<script>
var no = 5; // snow number
var speed = 15; // smaller number moves the snow faster
var snowflake = "snow.gif";

var ns4up = (document.layers) ? 1 : 0; // browser sniffer
var ie4up = (document.all) ? 1 : 0;
var dx, xp, yp; // coordinate and position variables
var am, stx, sty; // amplitude and step variables
var i, doc_width = 400, doc_height = 500;
if (ns4up) {
doc_width = self.innerWidth;
doc_height = self.innerHeight;
} else if (ie4up) {
doc_width = 500;
doc_height = 500;
}
dx = new Array();
xp = new Array();
yp = new Array();
am = new Array();
stx = new Array();
sty = new Array();
for (i = 0; i < no; ++ i) {
dx[i] = 0; // set coordinate variables
xp[i] = Math.random()*(doc_width-50); // set position variables
yp[i] = Math.random()*doc_height;
am[i] = Math.random()*20; // set amplitude variables
stx[i] = 0.02 + Math.random()/10; // set step variables
sty[i] = 0.7 + Math.random(); // set step variables
if (ns4up) { // set layers
if (i == 0) {
document.write("<layer name="dot"+ i +"" left="15" ");
document.write("top="15" visibility="show"><img src="");
document.write(snowflake + "" border="0"></layer>");
} else {
document.write("<layer name="dot"+ i +"" left="15" ");
document.write("top="15" visibility="show"><img src="");
document.write(snowflake + "" border="0"></layer>");
}
} else if (ie4up) {
if (i == 0) {
document.write("<div id="dot"+ i +"" style="POSITION: ");
document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: ");
document.write("visible; TOP: 15px; LEFT: 15px;"><img src="");
document.write(snowflake + "" border="0"></div>");
} else {
document.write("<div id="dot"+ i +"" style="POSITION: ");
document.write("absolute; Z-INDEX: "+ i +"; VISIBILITY: ");
document.write("visible; TOP: 15px; LEFT: 15px;"><img src="");
document.write(snowflake + "" border="0"></div>");
}
}
}
function snowNS() { // Netscape main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = self.innerWidth;
doc_height = self.innerHeight;
}
dx[i] += stx[i];
document.layers["dot"+i].top = yp[i];
document.layers["dot"+i].left = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("snowNS()", speed);
}

function snowIE() { // IE main animation function
for (i = 0; i < no; ++ i) { // iterate for every dot
yp[i] += sty[i];
if (yp[i] > doc_height-50) {
xp[i] = Math.random()*(doc_width-am[i]-30);
yp[i] = 0;
stx[i] = 0.02 + Math.random()/10;
sty[i] = 0.7 + Math.random();
doc_width = document.body.clientWidth;
doc_height = document.body.clientHeight;
}
dx[i] += stx[i];
document.all["dot"+i].style.pixelTop = yp[i];
document.all["dot"+i].style.pixelLeft = xp[i] + am[i]*Math.sin(dx[i]);
}
setTimeout("snowIE()", speed);
}

if (ns4up) {
snowNS();
} else if (ie4up) {
snowIE();
}
</script>