Yes, definitely check permissions. Also do note that to have the greatest success with images, they have to published-on-the-web in the most vanilla sense. Quickest way is that the end of the url is a .jpg or whatever file extension. But the real test is if you put in the URL on the address bar of your browser, it's just the image that comes out. I've found that some sharepoint urls for images (and teams might be worse) don't link directly to the image but to the sharepoint UX with the image in the middle.