我试过
$capabilities = DesiredCapabilities::htmlUnitWithJS();
$driver = RemoteWebDriver::create($host, $capabilities, 5000);
...
$driver->takeScreenshot('tmp.png');
但它失败并出现此错误
PHP致命错误：未捕获的异常＆＃39; UnknownServerException＆＃39;消息＆＃39; org.openqa.selenium.htmlunit.HtmlUnitDriver无法转换为org.openqa.selenium.TakesScreenshot＆＃39;在/cygdrive/c/Users/Chloe/workspace/Teads/php-webdriver/lib/WebDriverExceptions.php:79
（Google http://goo.gl/9SyjvO中没有结果。）这就是文档说使用它的方式。
https://github.com/facebook/php-webdriver/wiki/Taking-Full-Screenshot-and-of-an-Element
Selenium的版本是selenium-server-standalone-2.45.0.jar