/* creates a compressed zip file */
function create_zip($files = array(),$destination = '',$overwrite = false) {
 //if the zip file already exists and overwrite is false, return false
 if(file_exists($destination) && !$overwrite) { return false; }
 //vars
 $valid_files = array();
 //if files were passed in...
 if(is_array($files)) {
  //cycle through each file
  foreach($files as $file) {
   //make sure the file exists
   if(file_exists($file)) {
    $valid_files[] = $file;
   }
  }
 }
 //if we have good files...
 if(count($valid_files)) {
  //create the archive
  $zip = new ZipArchive();
  if($zip->open($destination,$overwrite ? ZIPARCHIVE::OVERWRITE : ZIPARCHIVE::CREATE) !== true) {
   return false;
  }
  //add the files
  foreach($valid_files as $file) {
   $zip->addFile($file,$file);
  }
  //debug
  //echo 'The zip archive contains ',$zip->numFiles,' files with a status of ',$zip->status;
  //close the zip -- done!
  $zip->close();
  //check to make sure the file exists
  return file_exists($destination);
 }
 else
 {
  return false;
 }
}

$files_to_zip = array(
 'preload-images/1.jpg',
 'preload-images/2.jpg',
 'preload-images/5.jpg',
 'kwicks/ringo.gif',
 'rod.jpg',
 'reddit.gif'
);
//if true, good; if false, zip creation failed
$result = create_zip($files_to_zip,'my-archive.zip');