I develop Unread (https://www.goldenhillsoftware.com/unread/).

I have some complex logic to find a hero image that is sometimes in a feed entry outside the HTML, and prepend it to the top of the article -- but only if there is not another reference to that image in the article. It is complicated because sometimes there will be hero-image.jpeg in the article and hero-image-1200x500.jpeg outside the article, and I have to judge whether the images are the same.

I am in favor of embedding the image into the HTML, and not adding it elsewhere.