To Forum Member:
Thank you for your help - you have solved the problem.
I was concentrating on all I had read recently about a red X being caused by security settings. You directed me to look elsewhere, and more carefully at the <img src code. And that is where the error was, not where I was concentrating.
On looking at this code this morning, I found an error that I just did not detect last night. The name of the .jpg file is really two words with an underscore between them. In error, I had typed the two words but with a hyphen (instead of the underscore) between them. However much I looked at it last night, I just did not detect this error.
I am most grateful for your help. Without it I should probably be still thinking I had a security settings problem.