<img src="http://placehold.it/400x200&text=No alt" />
<img src="http://placehold.it/400x200&text=Empty alt" alt="" />
<img src="http://placehold.it/400x200&text=With alt" alt="En placeholder bild" />
img:not([alt]) {
  border: 3px solid red;
}
img[alt=""], img[alt=''] {
  border: 3px solid orange;
}
Run Pen

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.