User defined string literals and namespace use
I would follow the way user-defined literals are used in the C++14 standard library: put them in a literals subnamespace that can be imported by the user. This subnamespace would be inline so that it can be imported alone, or automatically imorted when the namescape net is imported:

namespace net {
    class uri { ... }; // contains decomposed URI (path, parameters, etc)

    uri parse_uri(const std::string&amp; uri_str); // parse string and return uri instance

    inline namespace literals
    {
        uri operator "" _uri(const char*str, const unsigned long size)
        {
            return net::parse_uri(std::string{str, str + size});
        }
    }
}


Then, a client code could use your literal with the following code:

int main()
{
    // Import only the literal, not the rest of net
    using namespace net::literals;

    auto x = "/static/path/here/image.jpg"_uri;
}


I actually slightly simplified the way user-defined literals are used in the standard library for your example: there are actually nested inline namespaces in namespace literals so that a more precise selection of related literals can be done if needed (for example, import only the std::chrono-related literals). Since you have only one literal, you don't need to have so many nested namespaces, but you can still add them later if needed.