An image alt tag is important for several reasons.
First, image alt tags improve access to online information for users who are visually-impaired by converting on-screen content (text and images) to audio so they understand what content is on a webpage.
If an image has a correctly placed alt tag on it (or is “tagged”), a visually impaired person can use a screen reader to identify what an image is on a page when its called out by the reader.
Using the image of a “website development process” again as an example (see image above), when a person using a screen reader scrolls over it the reader will call out that the picture is “a diagram showing the website development process”.
If an image does not have a correctly placed alt tag on it, a visually impaired person might hear this instead – picture is “image 34021.jpg”
Images not tagged offer no information or value to site visitors using readers about the image or its purpose for being on the page.
Second, image alt tags help search engine crawlers understand the content and context of a webpage.
When indexing a website, part of the job of a search engine crawler is to analyze tagged images to help determine the topics and subject matter of the particular webpages the images are located on.
A third reason is image alt tags offer the opportunity to rank in Google Image results.
Google Images accounts for over 20% of all online searches and is the world’s second largest search engine – bigger than Bing and YouTube combined.
Descriptive image alt tags increase the likelihood that an image will be found by Google to be relevant and included in certain SERPs.
