Test image -

[Cormanus]

UPDATE: I've spent a good while this afternoon playing with this. According to the searching I've done on the Internet, Google Photos doesn't have support for linking from bulletin boards. Us users of Google Photos should pester them to fix that.

I tried a series of variations on the theme Guth identified, but I could make it work only when I dug out the link when not logged into Google and then only sporadically. In any event, for frequent linking, it's way too time consuming. I found reference to a fix using Google+, but I couldn't make that work consistently either.

Meanwhile, using another photo hosting site seems the easiest way around the problem and I'll explore the extension kennyw mentions, although I'm not sure I want to use imgur as well as two other sites.