In order to pass this test, convert all the images listed in this report into a modern image format such as JPEG 2000, JPEG XR or WebP.
It's important to understand that the modern image formats, like WebP, are not yet widely supported across all devices and browsers. You can find here a full list of supported browsers and devices for the WebP format.
If your target audience falls within one of the unsupported browser/device categories, you should serve optimized fall-back images in the original JPEG/PNG format so that your users don't see a broken or badly designed page:
<!--Before:--> <img src="image.jpg" alt=""> <!--After:--> <picture> <source type="image/webp" srcset="image.webp"> <img src="image.jpg" alt=""> </picture>
The browser uses the first listed source that's in a format it supports. If the browser does not support any of the formats listed in the "source" tags, it falls back to loading the image specified by the "img" tag.