$maxwidth) || ($maxheight && $pic_height > $maxheight))  {   if($maxwidth && $pic_width>$maxwidth)   {    $widthratio = $maxwidth/$pic_width;    $resizewidth_tag = true;   }    if($maxheight && $pic_height>$maxheight)   {    $heightratio = $maxheight/$pic_height;    $resizeheight_tag = true;   }    if($resizewidth_tag && $resizeheight_tag)   {    if($widthratio<$heightratio)     $ratio = $widthratio;    else     $ratio = $heightratio;   }    if($resizewidth_tag && !$resizeheight_tag)    $ratio = $widthratio;   if($resizeheight_tag && !$resizewidth_tag)    $ratio = $heightratio;    $newwidth = $pic_width * $ratio;   $newheight = $pic_height * $ratio;    if(function_exists("imagecopyresampled"))   {    $newim = imagecreatetruecolor($newwidth,$newheight);//PHP系统函数      imagecopyresampled($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);//PHP系统函数   }   else   {    $newim = imagecreate($newwidth,$newheight);      imagecopyresized($newim,$im,0,0,0,0,$newwidth,$newheight,$pic_width,$pic_height);   }    $name = $name.$filetype;   imagejpeg($newim,$name);   imagedestroy($newim);  }  else  {   $name = $name.$filetype;   imagejpeg($im,$name);  } }//使用方法：$im=imagecreatefromjpeg("./20140416103023202.jpg");//参数是图片的存方路径$maxwidth="600";//设置图片的最大宽度$maxheight="400";//设置图片的最大高度$name="123";//图片的名称，随便取吧$filetype=".jpg";//图片类型resizeImage($im,$maxwidth,$maxheight,$name,$filetype);//调用上面的函数

网上摘抄,还没做测试