Alt text helps search engines and the visually impaired understand what an image is about. The words used within an image’s alt attribute should be its text equivalent, and convey the same information or serve the same purpose that the image would. When a web page visitor hovers over the image, the text description will be shown in a small box.
The goal is to provide the same functional information that a visual user would see. The Alt text should function as a stand-in if the image itself is not available. Ask yourself if what text would provide the same information as the image.
Follow these tips to increase SEO with alt text:
- Every image on the page should have Alt text.
- This is mandatory for accessibility and for valid XHTML
- For images that play only a decorative role in the page, use an empty alt (e.g., alt=""), or a CSS background image so that reading browsers do not bother users by displaying text such as 'spacer image'
- Good Alt text is shorter than 65 characters (including spaces).
- The Alt text should be a short stand-in if the image itself is not available.
- The Alt text should accurately represent the image.
- It is important to use your keyword in the Alt text of your images. Search engines use the Alt text to help determine what an image is about.
- It is best to use the focus keywords in exactly the same order as you use them in the rest of the page (e.g. 'diabetes symptoms' is different than 'symptoms of diabetes'), but it is not mandatory. Using the words in the same order that searchers use is a strong indicator to them that the image is relevant to what they are looking for.
- You have only 65 characters (including spaces) to communicate what the image is about. Use the keyword just once.