Replace images by others with javascript

How can I replace images by others with javascript please ?

I've tried but something is wrong

 if ($(".grimm")) {
   $('.ch').
     html(
       $('.ch').
         html().
         replace('http://ift.tt/17zCwcL',
                 'http://ift.tt/1JNFH26')
   );
 }

<div class="grimm">
  <div class="ch">
    <img src="http://ift.tt/17zCwcL" />
  </div>
</div>