举例，如果原图是500x300, 缩略图是100x100， 如何让缩略图不变形，显示的是等比缩放后的局部；
$src = "1.jpg";
$info = getimagesize($src);
$type = image_type_to_extension($info[2],false);
$fun = "imagecreatefrom{$type}";
$image = $fun($src);
$target = imagecreatetruecolor(300,300);
imagecopy($target,$image,0,0,0,0,300,300);
$image_thumb = imagecreatetruecolor(100,100);
imagecopyresampled($image_thumb,$image,0,0,0,0,100,100,$info[0],$info[1]);
imagedestroy($image);
$image = $image_thumb;
header("Content-type: image/jpeg");
$funs = "image{$type}";
$funs($image_thumb);