You’ll almost never see them but they matter.
Back in the not-so-glory days of dialup, you’d often see the text of an alt tag while you waited for a few minutes for the page to load. Nowadays that’s rare, but alt tags remain just as important now as they ever have been.
Alt tags were originally created for screen readers. These are a type of web browser that read text for visually impaired visitors to your site. Since they have trouble seeing the image, they need a clear description of what the image is. Alt is, after all, ‘alternative text’.
You may not be particularly interested by screen readers but chances are you’re interested by how Google finds your website. The fact is that Google uses alt text to help its search algorithm better judge what images are and how they relate to a given search term.
The other image tag that matters for SEO is the Title attribute. It’s less important than the alt tag, but worth a mention as it creates the clever little box that shows the title of the image when a user hovers their mouse pointer over it.
As Matt Cutts, Google’s anti-spam head guru explains it, the importance of the alt tag is that it helps describe the scene and helps narrow down what the image is about.
The example he uses is that if you’re looking for an image of a cat next to a ball of yarn, just doing a search for “cat” isn’t going to find the best results. But if you search for “cat next to a ball of yarn” and the image helpfully has that information in the alt tag, it should take you right to it. It helps differentiate between a cat jumping, for example, and what you’re after – a cat sitting next to a ball of yarn.
The best way to add alt tags is to manually add them to your images. The WordPress uploader makes this very easy to do, as there’s an alt text field directly below the Caption field. In practice though, especially if your site has a load of images, it can become a chore to go into each image and add alternative tags. Luckily, there are plenty of plugins that can help – just search Google for Alt image WordPress plugins.
Some favourite plugins:
Other ways to boost your Image SEO
Its no secret that Google treats the alt tag as the most important textual information for images, but it’s not the only factor to consider. Some of the others that you have direct control over are the Title attribute, the filename, and the text content around the image on the page.
The built in media manager includes fields for Caption and Description. Use both of them if you want to, but at least in terms of SEO, neither is as important as the alt tag.