Want to hide the submit image button after clicking it in the webform

Hi I've a webform and have a image called submit which has the following code in it:

var Yes = submitform();
if (Yes)
{
  if (confirm('Press OK to Save & Process this request')) {
          document.forms["Content"].submit();
  }  
}

Everything works fine.. But the problem is sometmes the server response is slow and when the user clicks the submit button, there is a long delay before he gets to the confirmation form.  In this case the user is pressing submit button multiple times and multiple requests are being generated.
I want to hide the submit button as soon as the following happens.

After the user clicks OK to the above confirmation message  ==> confirm('Press OK to Save & Process this request')

How can this be done?
please advise
thanks
Kalios