调用方法：

$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;
    }
}
?>