What Is Image Optimization?

Optimization refers to the process of reducing file size while maintaining image quality so that files load quickly. Images that are not optimized before being uploaded for use on a site can slow down the site's load speed, causing visitors to leave.

Source: https://wordpress.com/ko/support/media/image-optimization/

An Example of an Unoptimized Image

So, what does an unoptimized image actually look like?

The image above uses an original 2048×1286 pixel image to render an element that is only 400 pixels wide. The actual file size of this image is a whopping 1.1MB. The browser has to request a massive 1.1MB image just to render something 400 pixels wide. The larger the image file, the longer the network request takes — and the longer users have to wait for the page to render, which seriously hurts the user experience.