Are the images optimized for their functions ?
Are the images used suitable for their display formats / sizes?
The volume of data exchanged for the presentation of an image depends on its size and the quality of its format. Some images have important information values, others are just illustration. The consumping of related resources must therefore be related to the importance of the image and allow audiences for whom the images are not accessible to understand their meaning.
Browser tools/consoles allow to check compliance w/ best practices (CHROME: extension greenIT : best practices)
6 other criteria related to the recommendation: Media engineering: reducing the digital service media as much as possible (images, animations, content, etc.)
Is a media management / use policy in place to reduce their impact, with criteria for media compression and formats ?
Are the number of fonts and the variants of fonts called (weight, characters used in the project) limited ?
Can the functionality be offered without calling external scripts or libraries (JS, AJAX, ...) ?
Does the target functionality require calling an iFrame ?
Can the native system features and components match as needed ?
Are videos and animations only used when they add value to the user ?