I also have this problem - frustratingly on the same page some images display and others do not - hard to see this as a cache issue
I've been experiencing this problem for months. Sometime images are there, sometimes not, and then sometimes they come back again. Imagine if Facebook users were reporting missing images and they were told to clear their caches.
The support answers I and others of you have received amount to gaslighting by technical support. "Problem? What problem? ... oh, uh ... just clear your cache." So much easier than doing the hard work of tracking down an intermittent, but immensely critical issue.
BTW, this is another VERY good reason to insist on really meaningful, detailed alt text for all images.
I could see why the images used in Course A quizzes might not load as images into quizzes that were imported into Course B unless the images in the Course A Files were also imported. In case it helps, I always upload any images that I use in my courses into my Course Files first - before using them in a quiz. Then, when importing content from one course to the next, I always import the Course Files images as well. Even so, I still run into this disappearing images issue periodically.
I raised this issue with Canvas and they recommended we white-list a list of Canvas services. We haven't implemented this yet, but are investigating this issue further before we make any changes. I use Chrome, and I have noticed that the images appear fine initially, but then if you leave the window open, navigate away from the images page, and open a different course, and then return to the same course over an hour later, this is when they tend to drop off.
The images seem to re-appear if you to a cache refresh using 'ctrl' + 'f5' in the browser.
I have also had this problem routinely. I contacted Canvas Chat, and they recommended clearing the cache. This fix only worked for a few days. I noticed this problem in Chrome; I was able to see the images in Firefox. I created a quiz that has images, and I am now concerned these quiz items may not appear for all students. I hope there is something Canvas can do to assist with a permanent fix. Maybe in the future Canvas may consider creating their own browser.
We are experiencing the same issue. Clearing the cache does work, but this is not an acceptable solution. We are using lots of images for our online and blended courses, but it is disappointing to realize that students may end up seeing a broken image icon instead. All of our images are in the Files sections of their respective courses. The "disappearing" images are random. One staff member may not see an image, while everyone else does. This is happening across Chrome and Safari web browsers for us. I'm not sure about Firefox since that is not used as often. Our students also report that Chrome and Safari are the most used browsers so we need images to consistently work on these browsers. I'll try to call Support the next time this happens to me and report it and request they screenshare and view the problem.
Just adding in our voice to this - we have had this issue as well and it is a tremendous disadvantage when planning online and blended courses which rely on images which are informational rather than decorative. As a workaround we've offered a link to the graphic as well as embedding it, but this is not ideal. Something is definitely going on here.
I ran into this in December 2017 and was told the issue was fixed. I'm wondering if something was done in the background again to break it.
----------message from 2017-----------------
Subject: Canvas Support: Images not appearing in Quizzes - Case #02668867
Thank you for contacting Canvas Support. I understand that file links within the Final Quiz are showing as broken when students take the Quiz. In looking into this it appears that this may have been in relation to a previous bug that has since been fixed. I can see that when I try resetting the links by embedding the image from the course files at this time it displays the image correctly. Please follow the steps in THIS guide to get those image links reset and please let us know if users are still reporting trouble with this so we can take a closer look if needed.