Okay, photos uploaded to Dropbox instead of Google Photos.
For future reference, this is what worked for me, using Dropbox:
Share → Create link
Open in incognito browser (regular browser doesn’t work)
Copy image address
Load into post
I still can’t see them. This is what it looks like now.
As mentioned here, copying images from Google Doc and pasting them seems to work reliably.
It would be good if there were more visible guides on how to post, as discussed in that thread.
Now they load.
The google docs method worked, but you can’t control image size.
I’m now using imgur, which should be recommended somewhere here for authors.
Pictures still don’t seem to be loading