An excellent solution for speeding up image load time on your website is to use Jetpack Plugin. You can search and install this plugin and post activating it with your WordPress.com account you can use dozens of it’s features.
One of the most used feature of Jetpack plugin is Photon which boosts websites image loading time in posts from the WordPress CDN. It cache the image on your website. When a user access a given post on your website, the image is not loaded from your server but from the super-fast network of WordPress.com. It reduces workload of your web server and thus improves overall performance of your website.
You can download Jetpack from here and upload it on to plugins area: https://wordpress.org/plugins/jetpack/
You can also search for Jetpack by WordPress.com and install it right away from the dashboard.