Is there any way that I can change the image on the fly in cgi?

[Abby]

To change images, from what I know, I need to add event handler into
the script (onMouseOver, onMouseOut ... etc), but I need to generate
it on the fly. I will have this javascript in my cgi file which will
be use to run dos program. The step in cgi script will be like below:

/*********************************************************/
Preload 50 images (each image will be name "image1" to "image50")
for ($i=0;$i<50;$i++){
run dos program and get output into array
if (output = ok){
change image$i to ok.jpg;
}
else {
change image$i to fail.jpg;
}
}
/*********************************************************/

Please let me know what to do. Thank you so much.