Hi there, @GrahamSmallwood ...
My question for you would be...how were the images in the course originally inserted into the content pages? Were they copy and pasted from another course? Are the images in your course "Files"? If you go to your course "Files" screen, check to see if the images for that course are listed somewhere on that page. If the images are not there, then that almost always suggests to me the images are located in some other course.
Here's another thing you can do...
Take a look at the course URL in the address bar of your browser ... especially the Course ID number in the URL. For example: https://SchoolName.instruture.com/courses/123456 where 123456 is your own Course ID number. Then, go to a page in your course that has images on it that you can view. Edit the page, and then click on the </> icon near the bottom right corner of the RCE (Rich Content Editor).
If you can find the HTML code for the image with the Course ID number, you can then compare it to the Course ID in your browser's address bar to see if it is the same. For example, the code might look like this:
<img src="https://SchoolName.instructure.com/courses/######/files/223.../download?wrap=1" alt="watering can" width="145" height="130" data-api-endpoint="https://SchoolName.instructure.com/api/v1/courses/#####/files/223..." data-api-returntype="File" />
If the number for the image in the code does not match the Course ID from your browser's address bar, then you would need to use the RCE tools to insert the image into the page ... so that when the course is imported/copied to other course shells, the images will work correctly.
I hope this might be of some help to you. Please let us know here in the Community if you have any questions along the way. Good luck!