Please try with this JavaScript which will find the img tags inside the default SharePoint tags  , will help you to change the S Thumb images to L Thumb or M Thumb images.

Map this JavaScript to master page.

$(window).load(function(){ $('.ms-profilepicture img').each(function () { $(this).attr('src', $(this).attr('src').replace('SThumb.jpg', 'LThumb.jpg')); })

$('.ms-peopleux-userImgDiv img').each(function () { $(this).attr('src', $(this).attr('src').replace('SThumb.jpg', 'LThumb.jpg')); }) });

Hope it works for you...!! enjoy... :)

Please try with this JavaScript which will find the img tags inside the default SharePoint tags, will help you to change the S Thumb images to L Thumb or M Thumb images.

Map this JavaScript to master page.

$(window).load(function(){
    $('.ms-profilepicture img').each(function () { 
        $(this).attr('src', $(this).attr('src').replace('SThumb.jpg', 'LThumb.jpg')); 
    }) 

     $('.ms-peopleux-userImgDiv img').each(function () { 
         $(this).attr('src', $(this).attr('src').replace('SThumb.jpg', 'LThumb.jpg')); 
    })
});

Hope it works for you.