Insérer une image dans un tableau en java-scr

Bonjour,
j'ai fait ce code pour un easyscroll le probleme c'es que je veut mettre des icones ou des images dans le tableau nav à la place de "Remonter", "Descendre", "Reinitialiser"

voila mon script

this.easyscroll = function(){

// id of the container element
var id = "myContent";

// navigation buttons text (le probleme est ici je veut mettre des images à la place des textes)
var nav = ["Remonter", "Descendre", "Reinitialiser"];

// id for each navigation button (OPTIONAL)
var navId = ["btnUp", "btnDown", "btnReset"];

// movement speed
var speed = 5;

// desired height of the container element (in pixels)
var height = 400;

//
// END CONFIG
// do not edit below this line (unless you want to of course :) )
//

var obj = document.getElementById(id);

obj.up = false;
obj.down = false;
obj.fast = false;

var container = document.createElement("div");
var parent = obj.parentNode;
container.id="easyscroll";
parent.insertBefore(container,obj);
parent.removeChild(obj);

container.style.position = "relative";
container.style.height = height + "px";
container.style.overflow = "hidden";
obj.style.position = "absolute";
obj.style.top = "0";
obj.style.left = "0";
container.appendChild(obj);

var btns = new Array();
var ul = document.createElement("ul");
ul.id="easyscrollnav";
for (var i=0;i<nav.length;i++){
var li = document.createElement("li");
li.innerHTML = nav[i];
li.id = navId[i];
btns.push(li);
ul.appendChild(li);
};
parent.insertBefore(ul,container);

btns[0].onmouseover = function(){
obj.up = true;
this.className = "over";
};
btns[0].onmouseout = function(){
obj.up = false;
this.className = "";
};
btns[1].onmouseover = function(){
obj.down = true;
this.className = "over";
};
btns[1].onmouseout = function(){
obj.down = false;
this.className = "";
};
btns[0].onmousedown = btns[1].onmousedown = function(){
obj.fast = true;
};
btns[0].onmouseup = btns[1].onmouseup = function(){
obj.fast = false;
};
btns[2].onmouseover = function(){
this.className = "over";
};
btns[2].onmouseout = function(){
this.className = "";
};
btns[2].onclick = function(){
obj.style.top = "0px";
};

this.start = function(){
var newTop;
var objHeight = obj.offsetHeight;
var top = obj.offsetTop;
var fast = (obj.fast) ? 2 : 1;
if(obj.down){
newTop = ((objHeight+top) > height) ? top-(speed*fast) : top;
obj.style.top = newTop + "px";
};
if(obj.up){
newTop = (top < 0) ? top+(speed*fast) : top;
obj.style.top = newTop + "px";
};
};
obj.interval = setInterval("start()",50);

};


//
// script initiates on page load.
//

this.addEvent = function(obj,type,fn){
if(obj.attachEvent){
obj['e'+type+fn] = fn;
obj[type+fn] = function(){obj['e'+type+fn](window.event );}
obj.attachEvent('on'+type, obj[type+fn]);
} else {
obj.addEventListener(type,fn,false);
};
};
addEvent(window,"load",easyscroll);