Are you using the advanced setting, not quick reply, and then click on manage attachments. Select choose file >> browse to the photo you want and select, then when selected those you want, you have to select 'upload', then wait until that's done, then select 'close this window', (top right usually), then, and only then, 'submit reply'...
Actually, I see your pics are just showing, to me anyway, as a small blue box, rather like the gifs RTF often uploads, which appear to not be working, so it might be the file size is too large as someone else suggested..?
The method you are using will not work. You are attempting to post a URL to [photos.google.com]. Even if I bypass this and attempt to access the URL directly, Google is telling me I'm not authorized to access your photo album.
Upload the picture instead of attempting to embed a URL redirect to another site.
To expand a bit on Shrew's posting above, when you use the [img]url[/img] protocol the url must point to a public picture hosting site. The one you used is password protected. Maybe you can make it public.
But since I don't use any of those picture websites, I just go to Advanced, click on the paper clip symbol above and upload my pic file. That way the file is stored on Trawlerforum, not a third party site where only you may have access to it.
I have been using the HTML [img]url[/img] protocol for years, with no issues, using "copy image address" function on Google Photos. And it works elsewhere, just not here.
Something changed somewhere, and I haven't changed any settings on Google Photos.
It seems to work on this photo, I was beginning to think maybe I and the guy behind me were getting close to the same life stage.
Here is the one I was trying to post, several times to no avail, and now it works. So I conclude it was some temporary TF thing.
"There's the Right Way, the Wrong Way, and what some guy says he's gotten away with"