//php自带函数 getimagesize()
$img_info = getimagesize('tomener.jpg');

echo '<pre>';

print_r($img_info);

输出：

Array
(
[0] => 170
[1] => 254
[2] => 2
[3] => width="170" height="254"
[bits] => 8
[channels] => 3
[mime] => image/jpeg
)
这次要用到的就是第四个元素了