What is the primary characteristic of raster images?

Raster images are primarily characterized by their dependence on pixels. Each pixel in a raster image represents a specific color value, and together, these pixels form the complete image. When you zoom in or enlarge a raster graphic, it may appear pixelated or blurry because enlarging it does not create new pixel information; instead, it stretches the existing pixels. This dependence on pixels is the fundamental aspect that distinguishes raster images from vector images, which are created using mathematical paths and can be resized without losing quality.

The other options do not accurately represent the characteristics of raster images. For instance, while vectors can be scaled infinitely, raster images lose quality upon scaling. Additionally, the size of a raster image isn't always smaller; it varies depending on resolution and color depth. Lastly, raster images are not limited to web use; they are used in various applications, including print media, photography, and digital art.