This is a moderately new trend for genre books, and it’s still more common for YA than adult SFF, but it’s lovely and complicated and much harder to do than it looks.
Anyhow, this cover trend seems to do a good job of incorporating small elements from the story–either as part of the frame itself or in the backdrop–without actually having a scene from the story acted out. And with these, generally the longer you look, the more you see.
Also, the typography happens to be important on these, especially in the case of The Forest Queen.
As much as I’d like to recreate this, I can’t seem to do so. (I tried to make some frames like this, but I honestly think this is currently above my pay grade!) For now, I’ll leave this for real artists!
(By the way, run out and purchase SISTERS OF THE WINTER WOOD! I blurbed that book and it was wonderful!)