/**
 *从$ inputFileName创建一个缩略图，不高于或宽
 * $ maxSize。 返回新图像资源或错误时返回false。
 * 
 * @param 
 * @arrange (512.笔记) jb51.cc
 **/
    function thumbnail($inputFileName,$maxSize = 100)
    {
        $info = getimagesize($inputFileName);
 
        $type = isset($info['type']) ? $info['type'] : $info[2];
 
        // Check support of file type
        if ( !(imagetypes() & $type) )
        {
            // Server does not support file type
            return false;
        }
 
        $width  = isset($info['width'])  ? $info['width']  : $info[0];
        $height = isset($info['height']) ? $info['height'] : $info[1];
 
        // Calculate aspect ratio
        $wRatio = $maxSize / $width;
        $hRatio = $maxSize / $height;
 
        // Using imagecreatefromstring will automatically detect the file type
        $sourceImage = imagecreatefromstring(file_get_contents($inputFileName));
 
        // Calculate a proportional width and height no larger than the max size.
        if ( ($width <= $maxSize) && ($height <= $maxSize) )
        {
            // Input is smaller than thumbnail,do nothing
            return $sourceImage;
        }
        elseif ( ($wRatio * $height) < $maxSize )
        {
            // Image is horizontal
            $tHeight = ceil($wRatio * $height);
            $tWidth  = $maxSize;
        }
        else
        {
            // Image is vertical
            $tWidth  = ceil($hRatio * $width);
            $tHeight = $maxSize;
        }
 
        $thumb = imagecreatetruecolor($tWidth,$tHeight);
 
        if ( $sourceImage === false )
        {
            // Could not load image
            return false;
        }
 
        // Copy resampled makes a smooth thumbnail
        imagecopyresampled($thumb,$sourceImage,$tWidth,$tHeight,$width,$height);
        imagedestroy($sourceImage);
 
        return $thumb;
    }
 
    /**
     * Save the image to a file. Type is determined from the extension.
     * $quality is only used for jpegs.
     * Author: mthorn.net
     */
    function imageToFile($im,$fileName,$quality = 80)
    {
        if ( !$im || file_exists($fileName) )
        {
           return false;
        }
 
        $ext = strtolower(substr($fileName,strrpos($fileName,'.')));
 
        switch ( $ext )
        {
            case '.gif':
                imagegif($im,$fileName);
                break;
            case '.jpg':
            case '.jpeg':
                imagejpeg($im,$quality);
                break;
            case '.png':
                imagepng($im,$fileName);
                break;
            case '.bmp':
                imagewbmp($im,$fileName);
                break;
            default:
                return false;
        }
 
        return true;
    }
 
    $im = thumbnail('temp.jpg',100);
    imageToFile($im,'temp-thumbnail.jpg');


/***   代码来自编程之家 jb51.cc（jb51.cc）   ***/