An alt tag is an HTML attribute applied to image tags in order to procure an alternative text for search engines. It is also knowns as "ALT Attribute" and "ALT Description".
Applying alt tags to images positively impacts search engine rankings.
Search engine robots cannot interpret images, therefore, ALT tags provide an opportunity for readability.
Alt tags are also beneficial for visitors on browsers that can't process images or on a screen readers' webpage.
Alt text is included in the image tag:
Product images have to be optimized for site speed and contain the same keywords like the product page.
The text should be kept short and include the topic to maximize its impact.
Avoid keyword stuffing, because popular search engines do not respond well to it.
Graphic Interchange Format (GIF) and Animated GIF
Portable Network Graphics (PNG)