Security tips you must know before use this function :

First : make sure that the file is not empty.

Second : make sure the file name in English characters, numbers and (_-.) symbols, For more protection.

You can use below function as in example

<?php

/**
 * Check $_FILES[][name]
 *
 * @param (string) $filename - Uploaded file name.
 * @author Yousef Ismaeil Cliprz
 */
function check_file_uploaded_name ($filename)
{
    (bool) ((preg_match("`^[-0-9A-Z_\.]+$`i",$filename)) ? true : false);
}

?>

Third : make sure that the file name not bigger than 250 characters.

as in example :

<?php

/**
 * Check $_FILES[][name] length.
 *
 * @param (string) $filename - Uploaded file name.
 * @author Yousef Ismaeil Cliprz.
 */
function check_file_uploaded_length ($filename)
{
    return (bool) ((mb_strlen($filename,"UTF-8") > 225) ? true : false);
}

?>

Fourth: Check File extensions and Mime Types that you want to allow in your project. You can use : pathinfo() http://php.net/pathinfo

or you can use regular expression for check File extensions as in example

#^(gif|jpg|jpeg|jpe|png)$#i

or use in_array checking as

<?php

$ext_type = array('gif','jpg','jpe','jpeg','png');

?>

You have multi choices to checking extensions and Mime types.

Fifth: Check file size and make sure the limit of php.ini to upload files is what you want, You can start from http://www.php.net/manual/en/ini.core.php#ini.file-uploads

And last but not least : Check the file content if have a bad codes or something like this function http://php.net/manual/en/function.file-get-contents.php.

You can use .htaccess to stop working some scripts as in example php file in your upload path.

use :

AddHandler cgi-script .php .pl .jsp .asp .sh .cgi
Options -ExecCGI  

Do not forget this steps for your project protection.

The destination directory must exist; move_uploaded_file() will not automatically create it for you.

Permissions issue.

If you have set a setgid I.e g+s on the folder and wondering why the created files are owned by www-data:www-data, note that uploaded files are first saved in /tmp folder with the web user.

The move_uploaded_file() command moves the files from /tmp to the given TO directory, including the current permissions the /temp file has.

Hence the setgid gets ignored and doesn't inherit the parent permissions.

For those using PHP on Windows and IIS, you SHOULD set the "upload_tmp_dir" value in php.ini to some directory around where your websites directory is, create that directory, and then set the same permissions on it that you have set for your websites directory. Otherwise, when you upload a file and it goes into C:\WINDOWS\Temp, then you move it to your website directory, its permissions will NOT be set correctly. This will cause you problems if you then want to manipulate that file with something like ImageMagick's convert utility.

When using move_uploaded_file(). If the user uploads an image with a name that already exists, move_uploaded_file() will overwrite it. It's a good practice to store images in directories that you generate upon creating ur card/user/product etc...

<?php
    function generateDir(int $n): string {
         $characters="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
        $dir = "";
        for($i = 0; $i<$n; $i++){
            $index = rand(0, strlen($characters)-1);
            $dir .= $characters[$index];
        }
        return $dir;
    }

    $image = $_FILES["image"];
    $imagePath = 'images/'. generateDir(10) .'/'. $image["name"];

    // Make the directory first or else it will not proceed with the upload.
    mkdir($imagePath);
    
    // some error handling etc...

    move_uploaded_file($image["tmp_name"],  $imagePath);
?>

If you're dealing with files uploaded through some external FTP source and need to move them to a final destination, searching php.net for "mv" or "move" won't get you what you want. You want the rename() function. 

http://www.php.net/manual/en/function.rename.php

(move_uploaded_file() won't work, since the POST vars won't be present.)

move_uploaded_file (on my setup) always makes files 0600 ("rw- --- ---") and owned by the user running the webserver (owner AND group).
Even though the directory has a sticky bit set to the group permissions!
I couldn't find any settings to change this via php.ini or even using "umask()".

I want my regular user on the server to be able to "tar cjf" the directory .. which would fail on files totally owned by the webserver-process-user;
the "copy(from, to)" function obeys the sticky-bit though!

nouncad at mayetlite dot com posted a function that uploaded a file, and would rename it if it already existed, to filename[n].ext

It only worked for files with extensions exactly three letters long, so I fixed that (and made a few other improvements while I was at it).

<?php
// Usage: uploadfile($_FILE['file']['name'],'temp/',$_FILE['file']['tmp_name'])
function uploadfile($origin, $dest, $tmp_name)
{
  $origin = strtolower(basename($origin));
  $fulldest = $dest.$origin;
  $filename = $origin;
  for ($i=1; file_exists($fulldest); $i++)
  {
    $fileext = (strpos($origin,'.')===false?'':'.'.substr(strrchr($origin, "."), 1));
    $filename = substr($origin, 0, strlen($origin)-strlen($fileext)).'['.$i.']'.$fileext;
    $fulldest = $dest.$newfilename;
  }
  
  if (move_uploaded_file($tmp_name, $fulldest))
    return $filename;
  return false;
}
?>

For those which will use inotify-tools to start an event when move_uploaded_file put the file in a specific directory, be aware that move_uploaded_file will trigger the create event, and not the move event of inotify-tools.

Just a helpful comment.  If you have open_basedir set then you must set upload_tmp_dir to somewhere within the open_basedir.  Otherwise the file upload will be denied.  move_uploaded_file might be open_basedir aware, but the rest of the upload process isn't.

It seems that move_uploaded_file use the GROUP permissions of the parent directory of the tmp file location, whereas a simple "copy" uses the group of the apache process. This could create a security nighmare if your tmp file location is owned by root:wheel

Ensure the upload temporary directory and the destination directory have "write" permissions for Other.