There doesn't seem to be any way to save Google Image search preferences, even when logged in to Google, which is a bit strange. I would have thought this would be something that a lot of people would use.
Something like this would work:
var searchTerm = prompt("Enter search term:","");
searchTerm = escape(searchTerm);
var url = "http://www.google.com/search?q=" + searchTerm + "&tbm=isch&hl=en&cr=&safe=images&orq=dog&tbs=isz:lt,islt:vga&biw=1280&bih=";
window.location.href = url;