What feature shows how a style affects the appearance of an image when the style is moused over in the picture styles gallery?

The feature that shows how a style affects the appearance of an image when moused over in the picture styles gallery is called "Live Preview." This functionality allows users to see a real-time preview of the selected style applied to the image without making any permanent changes. It helps in quickly assessing how different styles will alter the image's look, facilitating easier decision-making.