This is the first in a sequence of videos about images. It describes the fundamental principles of a bitmap image, namely, that a bitmap is a rectangular grid of picture elements known as pixels. It explains how pixel density, which is known as the image resolution, and the number of bits used to encode the colour of each pixel, which is known as the colour depth, can impact on the quality and file size of a bitmap image. The impact of metadata on the size of an image file is also mentioned.