<font color=skyblue>Well, TSR has the rule written up that the limit is 8 images total can be used on field. I was thinking that if 4 were gone, that casting a second spell would replinish only the lost four to give you the total max again at 8 (for a high level mage). </font>

I'd go with the 'doesn't stack' theory.

What would stop a mage casting ironskins to exhaustion every day?