Which of the following tools is used primarily for retouching images?

The Clone Stamp Tool is specifically designed for retouching images, making it the ideal choice among the options provided. This tool allows users to copy pixels from one part of an image and paint them over another area. This capability is particularly useful for removing blemishes, imperfections, or unwanted objects in a photograph, as you can replicate and blend the surrounding textures seamlessly.

In contrast, the Paint Bucket Tool is employed for filling areas with color, which does not address the nuances of image retouching. The Shape Tool is utilized to create geometric forms, while the Pencil Tool is primarily used for drawing and creating pixel-based art. Neither of these tools effectively contributes to the retouching process in the way that the Clone Stamp Tool does. Understanding the specific functions of each tool is crucial for effective image editing and retouching in Photoshop.