<html><head><script src="https://libs.baidu.com/jquery/2.1.4/jquery.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>