An image CDN is a way of serving images from the edge of the network. A CDN—or Content Delivery Network—is a network of servers that are strategically positioned all over the world.
By pushing your images to these servers, the images are in closer proximity to all geographic regions, meaning they travel a shorter distance before reaching users’ devices. This results in faster delivery times for your site.
Many image CDNs also include image optimization strategies like compression, resizing, etc. to make your images smaller before serving them to users. They also do smart device detection so they know exactly which type of image to serve to mobile vs desktop.