What do you call an image with a series of colored dots?

An image made up of a series of colored dots is commonly referred to as a "pointillist" image or a "dot matrix" image. In the context of digital graphics, it may also be described as a "pixelated" image, where each dot represents a pixel. This technique is often associated with the art movement known as pointillism, where small dots of color are applied to create a larger image.