How to batch edit multiple images to make square sized pictures with original image in center using php imagejpeg?

<?php
// WORKS FOR JPEG IMAGES ONLY. FOR PNG, change function names
// also create a folder named "out" in the $datadir folder
///only 4 lines to be edited
//1. dir in which your image files are present
$datadir="J:/dgcert/";
//2. Expected min. Width of the output file
$_outw=840;
//3. Expected min. Height of the output file
$_outh=840;
//4. output folder (inside datadir)
$outfolder= '/out/';
//5. force final size -- -- If set to 1/true then line 2 and 3 will become max sizes of output image
// TO BE DONE IN FUTURE . does not work as of now
$forcesize=0;
////// no more edits needed
$files=array_diff(scandir($datadir),array(".",".."));
foreach ($files as $file)
{
	if(is_file($datadir.'/'.$file)){		
$outw=$_outw;
$outh=$_outh;
$mugl_im= imagecreatefromjpeg($datadir.$file);
list($thiswidth, $thisheight)= getimagesize($datadir.$file);
if($outw<$thiswidth) $outw=$thiswidth;
if($outh<$thisheight) $outh=$thisheight;
if($outw<$outh)$outw=$outh;
if($outh<$outw)$outh=$outw;
//echo $width . $height;exit;
$thumb = imagecreatetruecolor($outw, $outh);
//white color rgb
$bg = imagecolorallocate ( $thumb, 255, 255, 255 );
imagefilledrectangle($thumb,0,0,$outw,$outh,$bg);
imagecopyresized($thumb,$mugl_im,ceil(($outw-$thiswidth)/2),ceil(($outh-$thisheight)/2),0,0,$thiswidth,$thisheight,$thiswidth,$thisheight);

imagejpeg($thumb,$datadir.$outfolder.$file);
imagedestroy($thumb);
imagedestroy($mugl_im);
	}
}

?>