Photos not displaying when email is opened in Apple Mail app

I have started using the "insert from URL" function for photos from time to time. However, we have noticed that the Apple Mail app (on phone and desktop) is substituting those photos with a blue question mark. It works fine on a browser and the Google Mail app. Even forwarding from one account to another results in the Apple Mail images always turning into question marks and the other browsers/apps looking like they should. Is this something in the Apple Mail settings that we can't control?