About Responsive Image Test

This test will check if all of your page's images are appropriately sized for your user's viewport. Ideally, your page should not serve images that are larger than the version that's rendered on the user's screen. Serving an image larger than the user's viewport results in scaling down the image, use of unnecessary bandwidth, and slower page load time.

This issue can be fixed by using responsive images, which relies on creating multiple versions of each image, that are served via CSS media queries depending on the user's viewport dimensions.

Another solution can be to use vector-based image formats like SVG. SVG images scale appropriately to any size, without wasting unnecessary bandwidth. Also consider image CDNs that can help serve responsive images.