var check=0;

f0=new Image(); f0.src="images/Studmt0.jpg";
f1=new Image(); f1.src="images/Studmt3.jpg";

function c1()
{ 
  window.document.images[1].src=f1.src;
}

function c2()
{ 
  window.document.images[1].src=f0.src; 
}