In which situation is a contrast ratio not required?

The scenario where a contrast ratio is not required is when text overlays a graphic that conveys the same information. In this situation, the graphic itself provides meaningful context that allows users to understand the message without depending solely on the text. As a result, the necessity for a specific contrast ratio diminishes because the information is redundantly conveyed through the graphic, making it accessible even if the text does not stand out against the background.

The other options present situations where contrast is relevant to readability and accessibility. Decorative fonts can hinder readability and may require careful attention to contrast to ensure that the text remains legible. Larger text sizes can improve visibility, but they often still require consideration of contrast to ensure they meet accessibility standards, especially in diverse environments. Lastly, while categorizing graphics is important for accessibility, it does not directly relate to the requirement for contrast ratios.