Several ways to determine the file type of uploaded files in PHP

/**
 desc: Determine the uploaded file type
 link: bbs.it-home.org
 date: 2013/2/24
*/
$array = array('jpg','gif','png','jpeg');
$picImg = '/upfile/upload_pic/thumbnail_1258615556.jpg';
$img = strtolower($picImg);
//Method 1 to get the file extension
 $ext = substr($img,strrpos($img,'.')+1);//Here is the code to read the file extension
//How to get the file extension 2
$ext = end(explode('.',$img));
//Method 3 of getting the file extension This should be the safest, use php $ _FILES['type']
$ext = $_FILES['file']['type'];
//Method 4 to get the file extension
$ext = getimagesize($img );//This function returns an array
if( !in_array( $ext,$array ) )
{
 exit('The thumbnail address is wrong, please re-upload!');
 }
else
{
 echo('The file type you uploaded is not allowed');
 exit;
}
/*
 strtolower Convert uppercase characters to lowercase
 substr character interception, right Chinese processing is not friendly.
 strrpos Determine the position where characters appear in the specified string
 explode split function, return the result as an array
 end Read the last value of the data
 $_FILES Global variable file upload
 getimagesize Get the type of image
 in_array Determine whether the variable is in the array Medium
 exit terminates the current script running
*/
?>