This rule triggers when PageSpeed Insights detects that the images on the page can be optimized to
reduce their filesize without significantly impacting their visual quality.
Images often account for most of the downloaded bytes on a page. As a result, optimizing images can
often yield some of the largest byte savings and performance improvements: the fewer bytes the
browser has to download, the less competition there is for the client's bandwidth and the faster
the browser can download and render content on the screen.
Finding the optimal format and optimization strategy for your image assets requires careful analysis
across many dimensions: type of data being encoded, image format capabilities, quality settings,
resolution, and more. In addition, you need to consider whether some images are best served in a
vector format, if the desired effects can be achieved via CSS, and how to deliver appropriately
scaled assets for each type of device.
To answer these and other questions please follow the
image optimization guide
on Web Fundamentals. For a quick overview, see the
image optimization checklist