I just checked out Feedly, and it seems to use an illustration from the article when it can, a topic related generic illustration as an alternative (vague picture of an aeroplane say), or nothing.

You could use it as a model.

Not directly connected to this platform, but if I see an AI-generated image against a story I automatically assume the writer has taken as much care with their text as with their image and close the tab.

No images at all please. Hacker News feels so good (IMO) in part because there is very little extra fluff. No images is part of that.