<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<img src="" alt="">
<script>
var img = document.querySelector('img');
var now = new Date();
var day = now.getDay();
if(day === 0) img.src = "0.jpg";
if(day === 1) img.src = "1.jpg";
if(day === 2) img.src = "2.jpg";
if(day === 3) img.src = "3.jpg";
if(day === 4) img.src = "4.jpg";
if(day === 5) img.src = "5.jpg";
if(day === 6) img.src = "6.jpg";
</script>
</body>
</html>
</body>
</html>