Aqui te dejo este Codigo !!!! funciona al 100%%%
<?php
$imagen_original = 'http://a4.sphotos.ak.fbcdn.net/hphotos-ak-snc7/385685_370119443025748_971041911_n.jpg';
$imagen_th = 'th_' . $imagen_original;
$ancho_th = 100;
$alto_th = 80;
$calidad = 100;
//redimensionar imagen
$imagenjpeg = CroppedThumbnailJPEG($imagen_original,$ancho_th,$a lto_th);
//guardar en directorio actual
imagejpeg($imagenjpeg,$imagen_th,$calidad);
imagedestroy($imagenjpeg);
//mostrar
echo "<p>Imagen original: </p><img src='$imagen_original' /></p>";
echo "<p>Imagen miniatura: </p><img src='$imagen_th' /></p>";
function CroppedThumbnailJPEG($imgSrc,$thumbnail_width,$thu mbnail_height) {
//getting the image dimensions
list($width_orig, $height_orig) = getimagesize($imgSrc);
$myImage = imagecreatefromjpeg($imgSrc);
$ratio_orig = $width_orig/$height_orig;
if ($thumbnail_width/$thumbnail_height > $ratio_orig) {
$new_height = $thumbnail_width/$ratio_orig;
$new_width = $thumbnail_width;
} else {
$new_width = $thumbnail_height*$ratio_orig;
$new_height = $thumbnail_height;
}
$x_mid = $new_width/2; //horizontal middle
$y_mid = $new_height/2; //vertical middle
$process = imagecreatetruecolor(round($new_width), round($new_height));
imagecopyresampled($process, $myImage, 0, 0, 0, 0, $new_width, $new_height, $width_orig, $height_orig);
$thumb = imagecreatetruecolor($thumbnail_width, $thumbnail_height);
imagecopyresampled($thumb, $process, 0, 0, ($x_mid-($thumbnail_width/2)), ($y_mid-($thumbnail_height/2)), $thumbnail_width, $thumbnail_height, $thumbnail_width, $thumbnail_height);
imagedestroy($process);
imagedestroy($myImage);
return $thumb;
}
?>