ZMIANA TŁA, jak zmienić funkcję... Opcje

[miqa1984]

Witam,
mamy następujący skrypt do zmiany tła:
<script type="text/javascript">


//Set expiration in days, use 0 for session only cookie
var exp=20

//Set Background Images Array, use at least two Images.
//Do NOT use =, +, -, or spaces in path or filenames.
//For best results, set body's background to the first entry
var backgs=new Array
backgs[0]="photo1.jpg"
backgs[1]="photo2.jpg"
backgs[2]="photo3.jpg"

/////////No Editing Needed for rest of Script////////
function bgChange(){
if (backgs.length==0)
backgs.push([backgs.shift()])
for (i = 0; i < backgs.length; i++)
if (document.body.background!==backgs[i]||document.body.style.backgroundImage.toLowerCase()!=='url('+backgs[i].toLowerCase()+')'){
document.body.style.backgroundImage='url('+backgs[i]+')'
break
}
}

function get_cookie(Name) {
var search = Name + "="
var returnvalue = "";
if (document.cookie.length > 0) {
offset = document.cookie.indexOf(search)
if (offset != -1) {
offset += search.length
end = document.cookie.indexOf(";", offset);
if (end == -1) end = document.cookie.length;
returnvalue=unescape(document.cookie.substring(offset, end))
}
}
return returnvalue;
}

function onloadfunction(){
var acookiename="abgchange"
var acookievalue=get_cookie(acookiename)
if (acookievalue!=""){
backgs=eval(acookievalue)
document.body.style.backgroundImage='url('+backgs[0]+')'
}
}

function saveBgrnd(){
var abackgs='["'
for (i = 0; i < backgs.length; i++)
abackgs+=backgs[i]+'","'
abackgs=abackgs.substr(0,abackgs.length-2)+']'
var acookiename="abgchange"
var date = new Date();
date.setTime(date.getTime()+(exp*24*60*60*1000));
var expires = exp? "; expires="+date.toGMTString() : ""
var acookievalue=abackgs+expires+"; path=/"
document.cookie=acookiename+"="+acookievalue
}

if ( typeof window.addEventListener != "undefined" )
window.addEventListener( "load", onloadfunction, false );
else if ( typeof window.attachEvent != "undefined" ) {
window.attachEvent( "onload", onloadfunction );
}
else {
if ( window.onload != null ) {
var oldOnload = window.onload;
window.onload = function ( e ) {
oldOnload( e );
onloadfunction();
};
}
else
window.onload = onloadfunction;
}

window.onunload=saveBgrnd

</script>
<input type=button value="1" onClick="bgChange()">
<input type=button value="2" onClick="bgChange()">
<input type=button value="3" onClick="bgChange()">



no i zastanawiam się jak zrobić aby po kliku w btn 1 ustawiało się tło z obrazka photo1, jak kliknę w btn 2 żeby ustawiało się tło z obrazka photo2 i jak klikną w btn 3 żeby ustawiało się tło z obrazka 3, a nie tak jak do tej pory losowo.
Z góry dziękuję za pomoc.