It’s not just the text on your website that you need to think about in terms of search engine optimization; images can and should also be optimized and images are an increasingly important part of the SEO puzzle.
Failing to optimize the images on your site means losing out on a better page ranking for your website; it’s a common oversight which can fortunately be remedied quite easily.
Alt is an attribute attached to images on your site in its HTML/XML code. Search engine crawlers can’t see your site’s images; but they can see your alt attributes. This is also a matter of accessibility, since the visually impaired also use this information to find out what images your site features. You should use alt attributes for every image on your site as well as descriptive text and/or captions above or beneath images (when appropriate).
Alt attributes for images are commonly abused by unethical SEO firms and webmasters who are new to search engine optimization. Rather than using human-readable, descriptive text, they will cram these attributes with keywords, including ones which are irrelevant to their site in an effort to gain an edge in the search engine rankings.
This should be avoided. Having a high keyword density is simply not as effective as it once was for SEO purposes – and too high of a density or using irrelevant keywords can result in a lower, rather than a higher page ranking.
It also reduces the accessibility of your site to the visually impaired, who use web browsers in conjunction with text to speech engines which read the content of your site out loud, including any alt attributes for images. The end result is alienating any visitor using a screen reader or text-only browser, not to mention risking a lower ranking for your site.
What should be contained in an alt attribute?
The alt attribute for an image shouldn’t be a caption; instead, this attribute should contain descriptive information which explains what is pictured or that provides the same information as one would learn by looking at the image.
When writing alt attributes for images, ask yourself if your readers would be able to understand what these attributes were standing in for if the images on your site suddenly became unavailable; this should get you on the right track.
Alt attributes are required to pass XHTML validation, though it is fine to omit them when they serve a purely decorative function on your site. For example, if you have background images on your site which are part of your CSS, it’s probably not necessary to create alt attributes for them.
In the case of images which are used in place of text, such as search buttons or in navigation bars (something which isn’t recommended from a SEO or accessibility standpoint, as attractive as it can be), then the alt attributes for these images should make their function clear, rather than simply mentioning that they are a button.
One other thing you’ll want to take into account is the way that your alt attributes will actually be experienced by visually impaired visitors or those using text only web browsers. These attributes will be read or viewed as if they were part of the surrounding text, so it’s a good idea to try to make them flow naturally with the rest of the content in as far as this is possible.
There are accessibility standards in use by the EU and the United States which webmasters can refer to in designing their alt attributes; this is highly recommended.
Optimizing images for Google Image Search
Using alt attributes properly also helps images from your site to be found more easily by using image search engines, especially Google image search. While accessibility is an important reason for using alt attributes for your images, it’s always a good idea to make your website easy to find through as many channels as possible – whether they get there via a web search or an image search, traffic is traffic.
In order to optimize your images for these searches, you should make sure to give your images file names which are descriptive and preferably containing keywords which you use on your site. It’s actually pretty simple, but can make a big difference in terms of your site’s visibility.
Using alt attributes is something you can implement with a minimal amount of time and effort which can give a boost to your page rank and bring in more traffic almost immediately. Ignore alt attributes for images if you will – but you’ll be doing so at your own peril.