Did you execute the command above literally? Please keep in mind that you should replace
yourlearningsite.com with your web domain (e.g.
learning.onlineschool.com). You can also use a public IP if that's how you access CanvasLMS.
If you're still facing problems, could you try to manually right-click on the image, click on the URL and access it on your browser (the same thing you did here)?
That image should be accessible. If it is not, probably you did not use the correct web domain or there is any issue, such as the certificate not being properly configured for that domain.
Could you let us know of the results?