<!DOCTYPE html>
<html>
<head>
<script src="/lib/jquery-1.12.2.min.js"></script>
<script>
$(document).ready(function(){
$("button").click(function(){
$("img").attr("width",function(n, v){
return v - 50;
});
});
});
</script>
</head>
<body>
<img src="img_pulpitrock.jpg" alt="Pulpit Rock" width="284" height="213"><br>
<button>Decrease image width by 50px</button>
</body>
</html>