Why the audit is important
WebP is a new image format that provides better lossy and lossless compression for images on the web, compared to PNG and JPEG. Encoding your images in WebP rather than JPEG or PNG means that they will load faster and consume less cellular data. See A New Image Format For The Web for more on WebP.
How to pass the audit
Click View Details to see the potential savings of encoding your page's images with WebP rather than JPEG or PNG. To pass this audit, encode all of these images in WebP.
Browser support is not universal for WebP. You'll need to serve a fallback PNG or JPEG image when WebP is not available. See How can I detect browser support for WebP? for an overview of fallback techniques.
How the audit is implemented
This section explains how this audit is implemented, so that you can understand how the audit's score is calculated.
Lighthouse collects each JPEG and PNG image on the page, and then converts each to WebP. Lighthouse omits the image from its report if the potential savings are less than 8KB.