accept header in ajax that returns [HTTP_ACCEPT]=>*/*

I need to get the accept header as image/webp but instead I get only /.

How to do it in Ajax request? It happens in Ajax page only please some one help me to do it in Ajax PHP.

My Ajax code is

function showResult(str){
    if (str == '') {
      $('#clear').hide();
    }else{
      $('#clear').show();
      $.ajax({
      url: "<?=tep_href_link('ajax_search.php') ?>",
      type: 'POST',
      data:{type:'adavnced_search',str:str},
      success:function(result){
        $("#livesearch").html(result);
        var numItems = $('.p_remove').length;

           $('#livesearch').slideDown('fast',function(){
          $('#overlay').css({'display' : 'block'});
        }); 
      }
    });
    }
  }

Please help to get the required accept format as image/webp.

You should define the required content type in "Accept" under "headers":

function showResult(str){
    if (str == '') {
      $('#clear').hide();
    }else{
      $('#clear').show();
      $.ajax({
      url: "<?=tep_href_link('ajax_search.php') ?>",
      type: 'POST',
      headers: {          
          Accept: "Image/webp"
      },
      data:{type:'adavnced_search',str:str},
      success:function(result){
        $("#livesearch").html(result);
        var numItems = $('.p_remove').length;

           $('#livesearch').slideDown('fast',function(){
          $('#overlay').css({'display' : 'block'});
        }); 
      }
    });
    }
  }