How to get MIME type of a file in PHP 5.5?

Make use of the finfo() functions.

A simple illustration:

<?php
$finfo = finfo_open(FILEINFO_MIME_TYPE);
echo finfo_file($finfo, "path/to/image_dir/image.gif");
finfo_close($finfo);

OUTPUT :

image/gif

^{Note : Windows users must include the bundled php_fileinfo.dll DLL file in php.ini to enable this extension.}