An Alt Attribute (or Alt Tag) is a way for you to give descriptions to your site’s images. Search engines aren’t able to look at an image and tell what it is about. Therefore, it is very important that you provide descriptions within the Alt Attribute so that they can scan, index, and rank your image accordingly.
To a search engine webcrawler and image represents a blank space on the canvas of a website. So by giving each image a description, you provide search engines with a frame of reference to understand what each image on your site is about.
In addition, Alt Tags are necessary from a usability perspective. Blind people (and people with other disabilities) are not able to easily distinguish what is in an image. Using an image alt attribute allows you to help screen readers and search engines understand the function of an image by providing a text equivalent for the object.
Example of an Alt Attribute:
<img src=””http://www.example.com/images/picture2.jpg”” alt=”””Pretty”” width=””50″” height=””50″” />