What is a responsive image?
Use of Responsive Images
In “Properly Size Image” tab of SeoChecker's Content Performance you will find a list of images of the analyzed page that can be modified in order to improve the page's performance.
Specifically, what is wrong with these images is the size: resizing them you can save some space, expressed in the tab in KiB (kibibytes).
How SeoChecker determines if the image is oversized
The work of SeoChecker consists in comparing the two sizes of each image present in the analyzed page: one of the original image and one of the rendered image.
How can I properly size my images?
Do not use images larger than the version rendered on the screen of the user: doing so, you seriously risk to reduce the speed of the page's loading and to waste bytes.
Instead use one of these solutions:
- responsive images: in this way, for each image it will be generated different versions; then, in your CSS or HTML you can indicate which one of the version to use, through viewport dimensions, media queries etc.
- image CDNs
- SVG images, namely vector-based image formats.