Answer 1

If the picture cannot be displayed for some reason, the alt attribute will show a text instead of the image.

Answer 2

Shawn hi,
Alt attribute is not just about an alternative text if the image cannot display.
It also , and importantly have purpose in SEO and accessibility (for sight impaired people, the alt text will be read out loud even if the image is displayed).

https://www.clickworker.com/2018/05/17/alt-attribute/