Pardon my terminology. The pages that I am having a problem with are Moodle pages that link from the main course page- lesson pages?
Students can see the pages (the url shows e.g., [moodle.mtsm.org]/mod/resource/view.php?id=xxx), just not the images, although they can see all the images on the course page. So I don't see how it could be a page access issue.
The image 'alt' text is displayed on the page, so the file request is seeing the image, just not displaying it for students.