Why do you need alt text on your images?

[dombowkett]

Because Google, Bing & Yahoo read only Alt text not images.

[MolviJi]

The alt tag tell about the image name and category.

[gurumaa]

ALT tags are also shown to the website visitor if for some reason their browser doesn't render the image. Screen readers for the visually impaired will read this text, making your image accessible. So, the ALT text does play a role in user experience since it tells the reader what the image is when they can't see it.

[maxbe]

Alt Tags also are known as alt attributes that used in HTML code to describe the appearance and function of an image on your website. Alt tags will be displayed in place of an image if an image file cannot be loaded. Alt tags provide better image context/descriptions to search engine crawlers, helping them to index an image properly. Adding alternative text to photos is first and foremost a principle of web accessibility.

[burling]

Image alt text is a title text of an image which helps search engine crawler to crawl all your website URLs as search engine bot unable to read any image.
By putting image alt text as a keyword, keyword density can be increased.