$originalDirectory = 'images';

$modifiedDirectory = 'result';

$files = array_diff( scandir( $originalDirectory ), array( '.', '..' ) );

foreach( $files as $file ) {

$startPath = $originalDirectory.'/'.$file;

$finalPath = $modifiedDirectory.'/'.$file;

if( !file_exists( $finalPath ) ) {

exec( 'greenscreen -t 22 -a 0 -b white '.$startPath.' "" '.$finalPath.'' );

}