Random Images In Gallery On Reload

I would like to create gallery of 6 images that will show random images on page reload without repeating them. I found some code on web, just changed path for images and added lightbox code. it looks like this, but it shows same image few times.

<script language="JavaScript">
<!--
/*
Random Image Script- By JavaScript Kit [URL]
Over 400+ free JavaScripts here!
Keep this notice intact please
*/
var myimages=new Array()
//specify random images below. You can have as many as you wish
myimages[1]="images/gallery/1.jpg"
myimages[2]="images/gallery/2.jpg"
myimages[3]="images/gallery/3.jpg"
myimages[4]="images/gallery/4.jpg"
myimages[5]="images/gallery/5.jpg"
myimages[6]="images/gallery/6.jpg"

for (i = 0; i < 6; i++) {
var ry=Math.floor(Math.random()*myimages.length)
if (ry==0)
ry=1
document.write('<a href="'+myimages[ry]+'" rel="lightbox"><img src="'+myimages[ry]+'">')
}
//-->
</script>