About this issue
The alt attribute is an important criterion for SEO. Search engines crawlers cannot parse graphic contents. That is why they use the alternative text to return consistent results, like in Google images.
The alt attribute is used in several cases unrelated to SEO:
- When a screen reader is used for accessibility purposes;
- While an image is loading, particularly on slow connections;
- When an image file is not found.
How to fix
Specify a relevant alternative attribute inside an <img> tag for each image on your website, e.g.
<img src="my-phone.jpg" alt="My phone description"/>
Some images do not define the alt attribute: