<!DOCTYPE HTML>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<style type="text/css">
*{transition:all 3s ease;}
</style>
</head>
<body>
<input type="button" id="click" value="тырк ^_^">
<div id="div" style="background:url('http://4.bp.blogspot.com/-KgZi-6zJrYM/UIzvvZmsDdI/AAAAAAAAAHI/tMpFQd9_Hf0/s1600/y_bda87ac1.jpg');width:500px;height:500px;background-repeat:no-repeat;background-size:cover;"></div>
<script type="text/javascript">
document.getElementById('click').onclick = function(){
document.getElementById('div').style.backgroundImage = 'url(http://trollface-fun.ru/wp-content/uploads/%D0%A5%D0%B8%D1%82%D1%80%D0%B5%D1%86-%D0%BC%D0%B5%D0%BC-face.jpg)';
}
</script>
</body>
</html>