$pi = pathinfo($imageFileName);
$filename = $pi['filename'];
$ext = $pi['extension'];

$thumbname = $filename.'-'.$width.'X'.$height.'.'.$ext;

$fspath = APPLICATION_PATH.'/..'.$path.'/'.$imageFileName;
$fspathThumb = APPLICATION_PATH.'/..'.$path.'/'.$thumbname;

if(!file_exists($fspathThumb)) {
thumb($fspath, $width, $height, $cwidth, $cheight, $fspathThumb);
}

return $publicpath.'/'.$thumbname;
}

function thumb($img, $w, $h, $cw='', $ch='', $thumb, $fill='') {
if (!extension_loaded('gd') && !extension_loaded('gd2')) {
trigger_error("No dispones de la libreria GD para generar la imagen.", E_USER_WARNING);
return false;
}

$imgInfo = getimagesize($img);
switch ($imgInfo[2]) {
case 1: $im = imagecreatefromgif($img); break;
case 2: $im = imagecreatefromjpeg($img); break;
case 3: $im = imagecreatefrompng($img); break;
default: trigger_error('Tipo de imagen no reconocido.', E_USER_WARNING); break;
}

if ($imgInfo[0] <= $w && $imgInfo[1] <= $h) {
$nHeight = $imgInfo[1];
$nWidth = $imgInfo[0];
}else{
if ($w/$imgInfo[0] < $h/$imgInfo[1]) {
$nWidth = $w;
$nHeight = $imgInfo[1]*($w/$imgInfo[0]);
$ny = ($h - $nHeight)/2;
}else{
$nWidth = $imgInfo[0]*($h/$imgInfo[1]);
$nHeight = $h;
$nx = ($w - $nWidth)/2;
}
}

$nWidth = round($nWidth);
$nHeight = round($nHeight);

$newImg = imagecreatetruecolor($nWidth, $nHeight);
$newImg = imagecreatetruecolor($w, $h);
$fillColor = imagecolorallocate($newImg, 0xFF, 0xFF, 0xFF);
imagefill($newImg, 0, 0, $fillColor);

imagecopyresampled($newImg, $im, $nx, $ny, 0, 0, $nWidth, $nHeight, $imgInfo[0], $imgInfo[1]);

switch ($imgInfo[2]) {
case 1: imagegif($newImg , $thumb); break;
case 2: imagejpeg($newImg, $thumb); break;
case 3: imagepng($newImg, $thumb); break;
default: trigger_error('Imposible mostrar la imagen.', E_USER_WARNING); break;
}

imagedestroy($newImg);
}