What tool allows for markup on documents in Image mode?

The image viewer serves as the essential tool that enables users to apply markup on documents within Image mode. It is specifically designed to handle images and provides functionalities that allow users to annotate, highlight, and make various edits directly to the visual content. This capability is vital for users who need to review or comment on graphical documents or images, as it offers intuitive interaction tailored for visual elements.

While the markup interface and highlight tool are related functionalities, they are typically found within the framework of document annotation in text-based environments rather than strictly in Image mode. The text editor is focused on modifying text content, without the capabilities suited for detailing images, making it less relevant in this context. Therefore, the image viewer is the most appropriate answer, as it is specifically built to facilitate interactions with documents in Image mode, allowing for effective markup and annotations.