We wrote an in-depth article on how to optimize your images for SEO. This page provides a high-level recap of this article.
altattribute, it is an alternative information for an image and improves the accessibility of your site.
Place images close to relevant text and place important images as high up in the code and page as possible.
Do not embed important text directly into an image
Adopt stable and descriptive URL structures
Avoid changing image URLs and apply 301 redirects if this is the case
Speed up image loading : Optimize image file size, use lazy-loading techniques, use responsive images.