All images have dimensions and size. Let's first talk about dimensions. As an example, image the shape of placemat. It has a rectangular shape with width and height measured in inches. Typically, the width is larger than the height. The placemat is just like an image. An image also has a width and height. However, in the computer world they're measured in pixels.

An image's width and height in pixels is called its "resolution". If an image has a resolution of 600x400 it has a width of 600 pixels and a height of 400 pixels.

Next, let's talk about image size. Size is determined typically by KB (Kilo Bytes) and MB (Mega Bytes). So, to determine an image's size you take the resolution, say 600x400, and multiply them together. In our example, we would have an image size of 600pixels x 400pixels = 240,000. This number is in Bytes. So, the size of our image would be 240KB.