Eventually worked out what as not working.

On the site where the images were working the source URL (img src) was full i.e. domain name/assets/images/file name etc. I used this on the second site, changing the domain name, but it did not work.  I removed the domain name part from the source  ie left it as img src /assets/images/file name.  This now worked and the images appeared.  Do not understand why one site needed the domain name and the other site did not.  Very Strange !!!