With so much of today’s standard SEO strategy emphasising the need to include your key search phrases as frequently as possible on your landing pages, how we label on-site images have started to follow suit. Many web-developers are simply using their key search terms as their image alt tags, ignoring the need to accurately describe the content of their photos.
It’s hard to see why this would be an issue; it makes sense that if a landing page organically ranks higher the higher the key search term frequency, introducing your key search terms into on-page image tags would increase your rankings. The small, incremental change in your rankings (if any at all) that would come from this practice isn’t worth the damage to the user experience that jamming your alt tags full of search terms can do. The most important questions to ask yourself when labelling your on-site images are: ‘are my labels informative?’ and ‘are my labels detailed?’
Google wants you to tell them as much as you can about your images. Detailed alt tags provide Google with the information they need to understand the content of your images and to determine whether or not to return your images to users on certain searches. The key benefit of alt tags, however, is that they provide users with an accurate description of your images to determine whether or not they wish to engage with your site – for on-site conversions, and for Google’s search engine algorithm, user engagement is key. From Google’s point of view, if your alt tags simply spam search terms, this will negatively affect your user engagement rating and consequently, have a negative effect on your organic rankings.
Below, Google’s own Matt Cutts provides a short, sweet and useful breakdown of how to create great alt text and details the technical importance of getting your alt tags right.