我通过使用SDK文件夹内以及PHP脚本内的key.json解决了它两次，

I solved it by using the key.json inside the SDK folder and also inside the PHP script, so two times.

Google官方云文档中的示例代码是完全没有价值的，即使正确初始化了SDK和PHP包，仍然会出现500错误.

And the example codes in the official google cloud documentation are completely worthless and are still giving 500 error even with SDK and PHP package correctly intialized.

我在github上找到了一个可以修改的工作代码:

I found a working code on github which I slightly modified:

require_once('../vendor/autoload.php');

use Google\Cloud\Vision\VisionClient;

$vision = new VisionClient([
    'projectId' => 'xxxx',
    'keyFilePath' => 'key.json'
]);

// Annotate an image, detecting faces.
$image = $vision->image(
    fopen('read.png', 'r'),
    ['text']
);

$tadaa = $vision->annotate($image);


echo '<pre>';
var_dump($tadaa->text());
echo '</pre>';

现在，经过许多小时的努力，终于奏效了！

Now after many hours of struggle it finally WORKS!