Php file image upload security - php

Question

$filename=$_FILES['file']['name'];
$type=$_FILES['file']['type'];
$extension=strtolower(substr($filename, strpos($filename, '.')+1));
$size=$_FILES['file']['size'];
if(($extension=='jpg' || $extension=='jpeg') && ($type!='image/jpg' || $type!='image/jpeg')){...
I have a input file, can let user upload jpg/jpeg image only, I have check type, extension, size.
However I'm not sure how to check if user change extension.(ex. abc.php -> abc.jpg)
any thing else I need to check before I save user's image into my server?

Answer 1

You can check the image with exif_imagetype()
http://www.php.net/manual/en/function.exif-imagetype.php
exif_imagetype() reads the first bytes of an image and checks its
signature.

Answer 2

I would suggest using finfo:
<?php
$finfo = finfo_open(FILEINFO_MIME_TYPE); // return mime type ala mimetype extension
foreach (glob("*") as $filename) {
echo finfo_file($finfo, $filename) . "\n";
}
finfo_close($finfo);
/* outputs:
text/html
image/gif
application/vnd.ms-excel
*/
?>
example taken from php document site.
see more info on the php document page http://www.php.net/manual/en/function.finfo-file.php

Answer 3

#Fabian's answer looks good for checking the type of file. While I would suggest a different approach to getting the extension of the file.
Consider a file named stack.overflow.jpg.
$filename = 'stack.overflow.jpg';
// With your code $extension = 'overflow.jpg'
$extension=strtolower( substr( $filename, strpos( $filename, '.' ) +1 ) );
// With pathinfo() $extension = 'jpg'
$extension = pathinfo( $filename, PATHINFO_EXTENSION );
Consider using pathinfo() to get the file extension: http://www.php.net/manual/en/function.pathinfo.php