Libreria GD

[luca200]

    function SaveProportionateImage($filename, $quality, $height, $width){ 

        $dest_image = imagecreatetruecolor( $width ,$height); 

        imagecopyresampled($dest_image, $this->src_image, 0, 0, 0, 0, 

            $width, 

            $height, 

            $this->src_width, 

            $this->src_height); 

        imagejpeg($dest_image, $filename.'.jpg', $quality); 

        imagedestroy($dest_image); 

    } 

Fatta al volo. Provala.