crear thumbanail PHP tamaño ajustado muy bueno.

thumbnail.php

<?php

/**
 * Funcion probado retorna miniatura con escala requerida.
 * @url http://stackoverflow.com/questions/11376315/creating-a-thumbnail-from-an-uploaded-image
 */

function makeThumbnails($updir, $img, $id)
{
    $thumbnail_width = 134;
    $thumbnail_height = 189;
    $thumb_beforeword = "thumb";
    $arr_image_details = getimagesize("$updir" . $id . '_' . "$img"); // pass id to thumb name
    $original_width = $arr_image_details[0];
    $original_height = $arr_image_details[1];
    if ($original_width > $original_height) {
        $new_width = $thumbnail_width;
        $new_height = intval($original_height * $new_width / $original_width);
    } else {
        $new_height = $thumbnail_height;
        $new_width = intval($original_width * $new_height / $original_height);
    }
    $dest_x = intval(($thumbnail_width - $new_width) / 2);
    $dest_y = intval(($thumbnail_height - $new_height) / 2);
    if ($arr_image_details[2] == 1) {
        $imgt = "ImageGIF";
        $imgcreatefrom = "ImageCreateFromGIF";
    }
    if ($arr_image_details[2] == 2) {
        $imgt = "ImageJPEG";
        $imgcreatefrom = "ImageCreateFromJPEG";
    }
    if ($arr_image_details[2] == 3) {
        $imgt = "ImagePNG";
        $imgcreatefrom = "ImageCreateFromPNG";
    }
    if ($imgt) {
        $old_image = $imgcreatefrom("$updir" . $id . '_' . "$img");
        $new_image = imagecreatetruecolor($thumbnail_width, $thumbnail_height);
        imagecopyresized($new_image, $old_image, $dest_x, $dest_y, 0, 0, $new_width, $new_height, $original_width, $original_height);
        $imgt($new_image, "$updir" . $id . '_' . "$thumb_beforeword" . "$img");
    }
}

bueno probado en www.dando-dando.com