In cards with large images, the CSS max-height and max-width property are effectively overridden by the way AnkiDroid handles large images (see here). For example, if the card template specifies

img {
  max-height: 120px;
}

for a very large image, AnkiDroid's automatic image rescaling overrides max-height, setting the image width/height to whatever AnkiDroid's built-in maximum size is, rather than what the user specified. This happens even if 120px is less than the maximum height, potentially causing the final image to be taller than 120px.