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One common suggestion concerning the search optimization of images is to use the alt attribute to place keywords relevant to the image contents.

I really loathe this.

If it was an amazing, perfect, incredible search optimization technique which would bring absolutely fantastic traffic I still wouldn’t recommend the technique. Appropriate alt attributes are one of the most critical areas for the user experience of screen reader users — using them inappropriately is a great way to give this section of your market a horrible experience on your site.

To be perfectly clear — most advocates of use of the alt attribute for image optimization do not advocate keyword stuffing or any other serious abuse of the alt attribute. However, to me, any recommended use of the attribute which does not place the user first is problematic.

Bluntly, if it’s really important that an image is described, then you should describe it in plain text, written out in a presentable and understandable manner. In the site content — not buried in the code.

I’m a firm believer that most images are purely decorative. They provide little to no information to a screen reader user, and the best choice is to leave the alt attribute empty. This means that the user agent can completely ignore the image — they can identify that there is an image present, and will also be aware that it does not need to be dealt with. (WebAIM: Designing for screen reader compatibility.) An absent alt attribute is dealt with differently — the user agent will attempt to identify the image via the src attribute:

How the JAWS screen reader announces image information

The behaviours detailed apply to JAWS version 6.2, 7.0, 7.1 and 8.0.

default behaviour for image with an alt attribute containing text
Announces presence of the image and the alt text
default behaviour for null alt text alt=""
Does not announce the presence of the image
default behaviour for an img without an alt attribute
Does not announce the presence of the image
default behaviour for image with an alt attribute containing text in a link
Announces presence of the image and the alt text
default behaviour for null alt text in a link alt=""
Does not announce the presence of the image
default behaviour for an img without an alt attribute in a link
Announces the presence of the image and the value of the src attribute

Steve Faulkner (Investigating the proposed alt attribute recommendations in HTML 5)

Now, the src attribute can be useful in certain situations – a well-named image file can be quite clear from this perspective. However, leaving the alt attribute blank will provide the best experience for insignificant images.

Significant images, on the other hand, are a completely different story. They do say that an image is worth 1,000 words…is it possible to do realistic justice to any significant image in an alt attribute?

My general take is that there are three types of images on the web:

  • Content-bearing text images,
  • Content-bearing non-text images,
  • and decorative images

The first is the only category which should have content in the alt attribute — and that text should be an exact duplicate of the text portrayed in the image. The second category should have additional descriptive information provided in the text, or a clear and obvious link provided to a more thorough description. The third should be left with an empty alt attribute. This is not significant information, and it should remain the user’s prerogative to enable the screen reader option which will provide them with additional image information.

The question with images and accessibility isn’t precisely a debate between whether images are content or not — instead, it’s the question whether images are useful content to those users with visual disabilities. The question you need to ask yourself is whether an alt attribute on the image will provide useful information to a user. Is it helpful to mark an image as “my cat” or “landscape of mountains with a flower in the foreground,” or does it simply add noise to the content?

This isn’t to say, however, that there aren’t perfectly reasonable ways to optimize for image search which won’t also interfere with the user experience with your website. Liana Evans recently published an article discussing image optimization at Search Engine Guide.

She does suggest using the alt attribute, but does at least emphasize moderation and specifically mentions accessibility as an issue to consider. The other four suggestions are all very sensible and simple ways to ensure that your images are available and easy to find. Li doesn’t mention the content surrounding the images in this article, although she does mention it in a Cre8asiteForums thread on image optimization. In this thread, Li specifically mentions that alt attribute use for image optimization is only a very slight influence.

On the whole, accessibility should always trump marketing. However, there really isn’t a huge divide between the two. In any circumstances I can imagine, there’s no search marketing benefit to choosing a less-accessible solution. Perhaps you’ll be less able to take advantage of some search engine loophole. This isn’t a serious loss for most businesses — there’s no guarantee that the same loophole will still be around next month, anyhow.

Further resources:

It’s important to note that these resources are intended to provide you with a wide variety of viewpoints on the subject. I think these articles are all worth reading; I don’t necessarily agree with them on every point.

Alt Attribute Use

Image Optimization