codice:
[img]/immagini/jpg/<%=(recordvisualizza.Fields.Item([/img]"
onload="w=this.width;h=this.height;if(w>30||h>30){if(w>h){h=Math.round(h/w*30);w=30}else{w=Math.round(w/h*30);h=30}this.width=w;this.height=h}"
/> 

Su piu' righe e indentato per la comprensione

w=this.width;
h=this.height;
if(w>30||h>30) { 
	if(w>h) {
		h=Math.round(h/w*30);
		w=30
	} 
	else {
		w=Math.round(w/h*30);
		h=30
	}
	this.width=w;
	this.height=h
}
ciao