Nominally, you can report such ads directly to the add vendor.
Anecdotally, I observe that if an image is less than full-width on the page, the ad inserting engine believes that it’s fair game for advertisement.
This may be exacerbated because some space is set aside in the content portion of the page for inline add that, to a less-that-sophisticated algorithm, would seem indistinguishable from intended content that happens to consist of an image.
Of course, the most annoying are the ones that start as a bottom-20-25% toast in the image, then expand (no interaction required) to play an animation in the full frame of the image, which finally resolves to a static image that doesn’t have a close option, leaving that part of the content completely obscured.
