Podrías usar algo como esto:
Código PHP:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
<title>Documento sin título</title>
</head>
<body>
<div id="canvas" style="position:absolute; left:-1500px; top:-1500px;">
<img src="img2/1.jpg" />
<img src="img2/2.jpg" />
<img src="img2/3.jpg" />
<img src="img2/4.jpg" />
</div>
<!-- crossbrowser images_loading_bar - Gerard Ferrandez - www.dhteumeuleu.com - Feb 2005 -->
<span id="LB0" style="position:absolute;left:50%;top:50%;"><span style="position:absolute;font-family:arial;font-size:10px;color:#ccc;background:#000;left:-50px;top:-18px">Loading...</span><span style="position:absolute;left:-50px;top:-5px;font-size:1px;width:100px;height:10px;background:#333"><span id="LB1" style="position:absolute;font-size:1px;width:0px;height:10px;background:#ccc"></span></span></span>
<script type="text/javascript">m00=document.getElementById("canvas").getElementsByTagName("img");m01=m00.length;function images_loading_bar(){m02=0;for(i=0;i<m01;i++)m02+=(m00[i].complete)?1:0;document.getElementById("LB1").style.width=Math.round(m02/m01*100)+'px';if(m02==m01)setTimeout("document.getElementById('LB0').style.display='none'",128); else setTimeout("images_loading_bar()", 64);};images_loading_bar();</script>
<!-- end of images_loading_bar code -->
</body>
</html>