While the header says 200 OK, the content of the file really is:
Content-Type: image/png
<html>
<head>
<title>404 Not Found</title>
</head>
<body>
<h1>404 Not Found</h1> The resource could not be found.<br /><br />
</body>
</html>
Version: wmf-deployment
Severity: normal
URL: https://upload.wikimedia.org/wikipedia/commons/thumb/0/09/Flag_of_South_Korea.svg/22px-Flag_of_South_Korea.svg.png