$resizeimage = new resizeimage("图片源文件地址", "200", "100", "0","缩略图地址");
//就只用上面的一句话,就能生成缩略图,其中,源文件和缩略图地址可以相同,200,100分别代表宽和高

//使用如下类就可以生成图片缩略图,
 
<?php
class resizeimage
{
  //图片类型
  var $type;
  //实际宽度
  var $width;
  //实际高度
  var $height;
  //改变后的宽度
  var $resize_width;
  //改变后的高度
  var $resize_height;
  //是否裁图
  var $cut;
  //源图象
  var $srcimg;
  //目标图象地址
  var $dstimg;
  //临时创建的图象
  var $im;
 
  function resizeimage($img, $wid, $hei,$c,$dstpath)
  {
    $this->srcimg = $img;
    $this->resize_width = $wid;
    $this->resize_height = $hei;
    $this->cut = $c;
    //图片的类型
  
$this->type = strtolower(substr(strrchr($this->srcimg,"."),1));
 
    //初始化图象
    $this->initi_img();
    //目标图象地址
    $this -> dst_img($dstpath);
    //--
    $this->width = imagesx($this->im);
    $this->height = imagesy($this->im);
    //生成图象
    $this->newimg();
    ImageDestroy ($this->im);
  }
  function newimg()
  {
    //改变后的图象的比例
    $resize_ratio = ($this->resize_width)/($this->resize_height);
    //实际图象的比例
    $ratio = ($this->width)/($this->height);
    if(($this->cut)=="1")
    //裁图
    {
      if($ratio>=$resize_ratio)
      //高度优先
      {
        $newimg = imagecreatetruecolor($this->resize_width,$this->resize_height);
        imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width,$this->resize_height, (($this->height)*$resize_ratio), $this->height);
        ImageJpeg ($newimg,$this->dstimg);
      }
      if($ratio<$resize_ratio)
      //宽度优先
      {
        $newimg = imagecreatetruecolor($this->resize_width,$this->resize_height);
        imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, $this->resize_height, $this->width, (($this->width)/$resize_ratio));
        ImageJpeg ($newimg,$this->dstimg);
      }
    }
    else
    //不裁图
    {
      if($ratio>=$resize_ratio)
      {
        $newimg = imagecreatetruecolor($this->resize_width,($this->resize_width)/$ratio);
        imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, ($this->resize_width)/$ratio, $this->width, $this->height);
        ImageJpeg ($newimg,$this->dstimg);
      }
      if($ratio<$resize_ratio)
      {
        $newimg = imagecreatetruecolor(($this->resize_height)*$ratio,$this->resize_height);
        imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, ($this->resize_height)*$ratio, $this->resize_height, $this->width, $this->height);
        ImageJpeg ($newimg,$this->dstimg);
      }
    }
  }
  //初始化图象
  function initi_img()
  {
    if($this->type=="jpg")
    {
      $this->im = imagecreatefromjpeg($this->srcimg);
    }
    if($this->type=="gif")
    {
      $this->im = imagecreatefromgif($this->srcimg);
    }
    if($this->type=="png")
    {
      $this->im = imagecreatefrompng($this->srcimg);
    }
  }
  //图象目标地址
  function dst_img($dstpath)
  {
    $full_length = strlen($this->srcimg);
 
    $type_length = strlen($this->type);
    $name_length = $full_length-$type_length;
 
 
    $name     = substr($this->srcimg,0,$name_length-1);
    $this->dstimg = $dstpath;
 
 
//echo $this->dstimg;
  }
}
?>