/* Select all images that
   are not children of a picture element */
img:not(picture *) {
  border: 3px solid red;
}
  

<img src="/examples/css-not/logos.png"
  alt="A Twitter, RSS and Twitch logo"
  width="508" height="201">
<picture>
  <source srcset="/examples/css-not/logos.webp"
    type="image/webp">
  <img src="/examples/css-not/logos.png"
    alt="A Twitter, RSS and Twitch logo"
    width="508" height="201">
</picture>