What is the main use of the 'alt' attribute in an image tag in HTML?

The 'alt' attribute in an image tag in HTML is primarily used to provide alternative text for an image when it cannot be displayed for some reason. This could occur due to various factors, such as slow internet connections, issues with the image file, or if a user is utilizing a screen reader due to visual impairments. The alternative text serves several important functions: it improves accessibility for users with disabilities, contributes to better SEO (search engine optimization) by providing context to search engines, and can also give insight into the content of the image to users who may not see it.

In terms of other options, while setting the width of an image, specifying the image source, and creating a link to the image are relevant attributes or actions in HTML, they do not pertain to the purpose of the 'alt' attribute. The 'width' attribute, for example, is used to control the size of the image, and the 'src' attribute is what directs the browser to where the actual image file is located. Thus, the primary and essential role of the 'alt' attribute is indeed to furnish a textual description that enhances usability and accessibility.