#! code

The following function will rename all of the image files in a directory to be sequential. The parameters are the path of the directory that the files are in and the name of a function that will be used to sort the array of files through the PHP usort() function.

function sequentialImages($path, $sort=false) {
 $i = 1;
 $files = glob($path."/{*.gif,*.jpg,*.jpeg,*.png}",GLOB_BRACE|GLOB_NOSORT);
 
 if ( $sort !== false ) {
  usort($files, $sort);
 }
 
 $count = count($files);
 foreach ( $files as $file ) {
  $newname = str_pad($i, strlen($count)+1, '0', STR_PAD_LEFT);
  $ext = substr(strrchr($file, '.'), 1);
  $newname = $path.'/'.$newname.'.'.$ext;
  if ( $file != $newname ) {
   rename($file, $newname);  
  }
  $i++;
 }
}

The following function can be used in the second parameter to sort the files by their last modified time.

function sort_by_mtime($file1, $file2) {
 $time1 = filemtime($file1);
 $time2 = filemtime($file2);
 if ( $time1 == $time2 ) {
  return 0;
 }
 return ($time1 < $time2) ? 1 : -1;
}

Putting these two function together we can call the sequentialImages() function like this.

sequentialImages('files','sort_by_mtime');

This function takes the following set of images:

file1.gif
file2.gif
wibble.gif
wobble.gif
02.gif

And renames them to the following:

01.gif
02.gif
03.gif
04.gif
05.gif