在我的测试中，我没有看到任何迹象表明这是错误的，但我不确定它是否存在会产生问题的边缘情况。

编辑 我看到它在使用 PHP 的 getimagesize 时抛出错误功能。

请您参考如下方法:

在使用协议(protocol)相对 URL 时发现了一个有趣的问题:

ou have to be careful to only use this syntax in pages destined for browsers. If you put it in an email, there will be no base page URL to use in resolving the relative URL. In Outlook at least, this URL will be interpreted as a Windows network file, not what you intended.

来自 here

基本上，只要请求是由浏览器而不是外部电子邮件客户端发出的，就没有正当理由说明这不应该起作用。

更多信息来自 here :

A relative URL without a scheme (http: or https:) is valid, per RTF 3986: Section 4.2. If a client chokes on it, then it's the client's fault because they're not complying with the URI syntax specified in the RFC.

Your example is valid and should work. I've used that relative URL method myself on heavily trafficked sites and have had zero complaints. Also, we test our sites in Firefox, Safari, IE6, IE7 and Opera. These browsers all understand that URL format