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Optimizing images is becoming more and more important in SEO (Search Engine Optimization) for websites. The ALT attribute is a critical step that is often overlooked. This can be a lost opportunity for better rankings.

In Google’s webmaster guidelines, they advise the use of alternative text for the images on your web site:

Images:. Use the alt attribute to provide descriptive text. In addition, we recommend using a human-readable caption and descriptive text around the image.

Why would they ask us to do that? The answer is simple, really; search engines have the same problem as blind users. They cannot see the images.

Many webmasters and inexperienced or unethical SEOs abuse the use of this attribute, trying to stuff it with keywords, hoping to achieve a certain keyword density, which is not as relevant for rankings now as it once was.

On the contrary, high keyword density can, on some search engines, trigger spam filters, which may result in a penalty for your site’s ranking. Even without such a penalty, your site’s rankings will not benefit from this tactic.

This method also puts persons who use screen readers at a greater disadvantage. Screen readers are software-based tools that actually read aloud the contents of what is displayed on the screen. In browsing the web, the alt attributes of images are read aloud as well.

Imagine listening to a paragraph of text which is followed by repetitions of many keywords. The page would be far from accessible, and, to put it bluntly, would be found quite annoying.

What exactly is an Alt attribute?

An ALT attribute should not be used as a description or a label for an image, though many people use it in that fashion. Though it might seem natural to assume that alternate text is a label or a description, it is not!

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.

The goal is to provide the same functional information that a visual user would see. The alt attribute text should function as a "stand in" in the event that the image itself is not available. Ask yourself this question: If you were to replace the image with the text, would most users receive the same basic information, and would it generate the same response?

Some examples:

  • If a search button is a magnifying glass or binoculars its alt text should be ’search’ or ’find’ not ’magnifying glass’ or ’binoculars’.
  • If an image is meant to convey the literal contents of the image, then a description is appropriate.
  • If it is meant to convey data, then that data is what is appropriate.
  • If it is meant to convey the use of a function, then the function itself is what should be used.

Some Alt Attribute Guidelines:

  • Always add alt attributes to images. Alt is mandatory for accessibility and for valid XHTML.
  • For images that play only a decorative role in the page, use an empty alt (i.e. alt="") or a CSS background image so that reading browsers do not bother users by uttering things like "spacer image".
  • Remember that it is the function of the image we are trying to convey. For instance; any button images should not include the word "button" in the alt text. They should emphasize the action performed by the button.
  • Alt text should be determined by context. The same image in a different context may need drastically different alt text.
  • Try to flow alt text with the rest of the text because that is how it will be read with adaptive technologies like screen readers. Someone listening to your page should hardly be aware that a graphic image is there.

Please keep in mind that using an alt attribute for each image is required to meet the minimum WAI requirements, which are used as the benchmark for accessibility laws in UK and the rest of Europe. They are also required to meet "Section 508" accessibility requirements in the US.

It is useful to categorize non-text content into three levels:

  • Eye-Candy
  • Mood-Setting
  • Content and Function

I. Eye-Candy

Eye-Candy are things that serve no purpose other than to make a site visually appealing/attractive and (in many cases) satisfy the marketing departments. There is no content value (though there may be value to a sighted user).

Never alt-ify eye-candy unless there is something there which will enhance the usability of the site for someone using a non-visual user agent. Use a null alt attribute or background images in CSS for eye-candy.

II. Mood-Setting

This is the middle layer of graphics which may serve to set the mood or set the stage as it were. These graphics are not direct content and may not be considered essential, but they are important in that they help frame what is going on.

Try to alt-ify the second group as makes sense and is relevant. There may be times when doing so may be annoying or detrimental to other users. Then try to avoid it.

For instance; Alt text that is identical to adjacent text is unnecessary, and an irritant to screen reader users. I recommend alt="" or background CSS images in such cases. But sometimes, it’s important to get this content in there for all users.

Most times it depends on context. The same image in a different context may need drastically different alt text. Obviously, content should always be fully available. The way you go in this case is a judgment call.

III. Content and Function

This is where the image is the actual content. Always alt-ify content and functional images. Title and long description attributes may also be in order.

The reason many authors can’t figure out why their alt text isn’t working is that they don’t know why the images are there. You need to figured out exactly what function an image serves. Think about what it is about the image that’s important to the page’s intended audience.

Every graphic has a reason for being on that page: because it either enhances the theme/ mood/ atmosphere or it is critical to what the page is trying to explain. Knowing what the image is for makes alt text easier to write. And practice writing them definitely helps.

A way to check the usefulness of alternative text is to imagine reading the page over the telephone to someone. What would you say when encountering a particular image to make the page understandable to the listener?

Besides the alt attribute you have a couple more tools at your disposal for images.

First, in degree of descriptiveness title is in between alt and longdesc. It adds useful information and can add flavor. The title attribute is optionally rendered by the user agent. Remember they are invisible and not shown as a "tooltip" when focus is received via the keyboard. (So much for device independence). So use the title attribute only for advisory information.

Second, the longdesc attribute points to the URL of a full description of an image. If the information contained in an image is important to the meaning of the page (i.e. some important content would be lost if the image was removed), a longer description than the "alt" attribute can reasonably display should be used. It can provide for rich, expressive documentation of a visual image.

It should be used when alt and title are insufficient to embody the visual qualities of an image. As Clark [1] states, "A longdesc is a long description of an image...The aim is to use any length of description necessary to impart the details of the graphic.

It would not be remiss to hope that a long description conjures an image - the image - in the mind’s eye, an analogy that holds true even for the totally blind."

Although the alt attribute is mandatory for web accessibility and for valid (X)HTML, not all images need alternative text, long descriptions, or titles.

In many cases, you are better off just going with your gut instinct -- if it’s not necessary to include it, and if you don’t have a strong urge to do it, don’t add that longdesc.

However, if it’s necessary for the whole page to work, then you have to add the alt text (or title or longdesc).

What’s necessary and what’s not depends a lot on the function of your image and its context on the page.

The same image may require alt text (or title or longdesc) in one spot, but not in another. If an image provides absolutely no content or functional information alt="" or background CSS images may be appropriate to use. But if the image provides content or adds functional information an alt would be required and maybe even a long description would be in order. In many cases this type of thing is a judgement call.

Image Search Engine Optimization Tips

Listed below are key steps in optimizing images:

  • Choose a logical file name that reinforces the keywords. You can use hyphens in the file name to isolate the keyword, but avoid to exceeding two hyphens. Avoid using underscores as a word separator, like for example "brilliant-diamonds.jpg";
  • Label the file extension. For example, if the image search engine sees a ".jpg" (JPEG) file extension, it’s going to assume that the file is a photo, and if it sees a ".gif" (GIF) file extension, it’s going to assume that it is a graphic;
  • Make sure that the text nearby the image that is relevant to that image.

Again, do not lose a great opportunity to help your site with your images in search engines. Use these steps to rank better on all the engines and drive more traffic to your site TODAY.


Google Image Search Help:

Related References:

[1] https://joeclark.org/book/sashay/serialization/Chapter06.html

About this SEO tutorial

This tutorial was written by John S. Britsios (aka Webnauts), Search Experience Consultant at SEO Workers and was published September 10, 2007.

Copyright reserved. Not to be reproduced.