People who know more about the topic than I do will argue for a default image for an online article for SEO and other reasons. Online pubs I've done stuff for would usually take a good/relevant photo if you have one. But, otherwise, would generally use some fairly generic stock graphic from some service they subscribed to.

Same goes for book covers. You probably need something unless you want to look really generic and cheap. But I'm mostly not going to pay a designer hundreds+ of dollars for a cover of an independently published book. I have had a former colleague who is actually good with this sort of thing do it in the past. I've also done a crappy job myself, done it in conjunction with a publisher (for whom I had the supply the cover image), and, yes, used generative AI/Photoshop.