Creating Accessible Images
Creating Effective Alternative (alt)Text

Overview

Most people are at least somewhat familiar with alt text. By the way, there is no such thing as an alt tag, though people often refer to alt text by this name. To be technically correct, it is the alt attribute of the <img> tag. Its name is not as important as its function, though, so let's take a look at what it means to have effective alt text.

The Importance of Alternative Text

One of the biggest accessibility problems on the Web today is the lack of alternative text for graphics and images. Individuals who are blind often use screen readers or refreshable Braille devices that read the text on the page to them. When these assistive technologies come across images without alt text, they are unable to communicate their meaning.

When a screen reader comes across an image with no alt attribute, there are a couple of things that could happen:

1. It could simply skip the image as if it were not even on the page.
2. It could find some text that is associated with the image such as the file name and read that instead.

The exact behavior of the screen reader varies between brands of screen readers and the circumstances of the Web page itself, but either way, the end result is undesirable. The user either misses the image content completely or gets some text that is probably meaningless.

Example: with alt text

Let's listen to Home Page Reader 3.0 reading the image—this time with alt text—so we can see the difference.

Select a format: Wav | Mp3 | RealMedia | Transcript

Here is the image that we were listening to:

The addition of alternative text allows screen reader users to get the same information as others who can see the image.

Adding alt Text

Let's look at another example image:

The HTML code for this image is as follows:

You can type the code exactly as you see it above into a text editor, or you can use the interfaces of software tools such as Dreamweaver, FrontPage, or GoLive to accomplish the same thing. In Dreamweaver, alt text is added through the Properties window as pictured below:

In Microsoft's FrontPage, you double click on the image to bring up the Picture Properties dialog box. You then add the text alternative to the Text field under Alternative representations.

Other editors have similar functions for adding alternative text. Consult your editor's documentation for instructions on how to add an alt attribute.

Now that we have a better idea of what an alt attribute is and how simple it is to add an alt attribute to an image, let's talk about what the alt attribute should contain.

How Images Are Used

Images on Web sites are used in three main ways:

1. to convey important content
2. to provide visual enhancements which offer no real content
3. to link to other areas of the site

The most appropriate alt text for an image depends on the way in which the image is used. In fact, the same image could be used for different reasons under different circumstances, and each instance of this image would have different alternative text. Keep the following rule in mind:

With that in mind, the most important information to convey in alternative text is that the user can click on this image to go to another area of the site.

Communicating the Purpose of the Graphic

Images that contain important content

If the image or graphic contains information that is relevant to the content of the site, then the alt attribute should also provide that content, in a way that is consistent with the purpose of the image. Remember that the purpose of the image is not necessarily the same as the appearance of the image.

Example 1

For example, the WebAIM Training CD site uses images for its main navigation, such as the one pictured below.

These images look like tabs on file folders. Some of these tabs are maroon, and others are blue. When the tab is selected, it turns white. Part of the text is in upper case; part is in lower case. All of these details are important to the look and feel of the Web site, but to someone who cannot see how the site looks, its look and feel are mostly irrelevant. The important aspect of these graphics is that they link to other areas of the site. With that in mind, I would want to provide alternative text that conveys the fact that the user can click on this image to go to another area of the site. In this case, the link destination would be Track 2 of the training event, which is the track for coordinators. The most appropriate alt text for this image is as follows:

"Track 2: Coordinators."

In this case, the alt text exactly matches the text in the graphic. In most cases where there is text within images, this is the best solution. Don't worry about describing the image. Tell the user about the purpose of the image, not its appearance.

Example 2

Take another look at the portrait of Silvia below:

This particular graphic could be used in many different ways, with many different purposes. Here are a few scenarios:

• An elementary school teacher creates a Web site to explain the difference between paintings, drawings, and sculpture. She includes several different examples of each type of art. In the text of the page itself, she describes the differences between these three media. She uses the portrait of Silvia as one of 4 examples of paintings. One possible alt text in this case would be "A painting of a young lady." This is probably sufficient, as long as the teacher has adequately described what a painting is within the document itself.
• A family member is compiling a list of people in her family, along with portraits of these individuals. Since all of the images are portraits, an appropriate alt text would be "Silvia Alvarez."
• An art instructor in a high school creates a Web site showing different types of paintings. He uses this painting as an example of a portrait, and explains within the text of the page what a portrait is. An appropriate alt text could be "Portrait."
• An art historian is creating a catalogue of different portrait artists. His purpose is to show portraits by various artists. The alt text could include information relevant to art historians, such as the title of the work of art, the name of the artist, the medium, and the date. The alt text could say "Silvia Alvarez, oil on canvas, by Paul Bohman, 2002."

We could go on with different scenarios, but I think you get the point. There is no one right alt text for any particular image. It all depends upon the context and the purpose of the image. This is a judgment call that the page's author must make.

Accuracy and brevity

Alternative text for images should be as accurate and as succinct as possible. Make sure that your alt text conveys all of the important information relevant to its purpose, but don't burden users with excessively long alt text. Screen readers or refreshable Braille devices always read the alt text, which can make image-heavy pages rather long. If you need a longer description of the image, you should add a longdesc tag to the image.

Null alt text

Decorative images

The Web has become a graphical environment in which developers often add images to their pages simply to enhance the visual appeal of the site. For example, the image below could be used to form part of a rounded border on a page.

Images in this category do not provide any content to the user; they are simply used for decorative purposes. These images have no value to someone who cannot see the page. The proper HTML markup for this type of image is what is often referred to as an empty or null alt attribute, written as alt="". That is alt equals quote quote, with no space in the middle. The source for the image in this example would look like this:

<img src="corner.gif" width="84" height="90" alt="" />

Screen readers will ignore graphics with empty alt text, which is exactly what we want in this case. You may be wondering why it is necessary to specify a null alt text. Wouldn't it make more sense to simply leave the alt attribute off entirely? This is a good question, but the answer is that missing alt text is worse than null alt text because some screen readers read the file name of the image, which can be confusing to listen to. When you add null alt text, screen readers skip over the image without reading anything at all.

Dreamweaver MX allows users to create null alt text within the Properties dialogue box.

Unfortunately, many other HTML editors do not allow you to create empty alt attributes within the graphical interface so you must edit your HTML source code directly. To do this, locate the image in the code and add alt="" to the img tag.

Transparent and spacer images

Developers often use transparent and spacer images to create space between elements on a page. Although users with sight do not see the transparent images, they may be visible to individuals using text browsers or screen readers. You should add an empty alt attribute (alt="") to all transparent and spacer images.

Redundant images

Sometimes, Web developers add alt text to an image that is exactly the same as the text next to it, or the same as another graphic next to it, as in the example below:

In cases like this, you should add null alt text, so that screen reader users do not have to hear the same information twice. The JAWS screen reader would say: "image, international students; image, international students" when reading this section of Web content, which can be confusing, or at least annoying. (In this case, both the photograph of the girl and the adjacent text are images.)

Image Maps

Client-side image maps

Every common Web development tool creates client-side image maps, rather than server-side image maps. As the names suggest, server-side image maps require special scripting on the server, whereas client-side image maps are processed only in the client's browser. Unless you have purposely chosen to create a server-side image maps, you probably will never create one. Client-side image maps can be accessible, whereas server-side image maps cannot.

Client-side image maps require alt text for both the image and the hot spots. Take a look at this example (Note: none of the links lead anywhere):

There is only one image above, but there are 5 hot spots. Each of these hot spots leads to a different location in the Web site, so it is necessary to convey the navigational purposes of each of the links. The alt text for these hot spots should be exactly the same as the text in the image. The alt text for the hot spots is HOME, Products, Services, Contact us, and Index. Now we have the alt text for the hot spots, but what about the image itself? Aside from the hot spots, this image does not convey any meaningful information. The most appropriate alt text for the image is a null alt text. Here is the code for the image and its hot spots:

<img src="imagemap.jpg" alt="" width="199" height="303" border="0" usemap="#Map"> <map name="Map">
<area shape="rect" coords="7,9,191,54" href="#maps" alt="HOME">
<area shape="rect" coords="7,68,191,114" href="#maps" alt="Products">
<area shape="rect" coords="7,127,190,172" href="#maps" alt="Services">
<area shape="rect" coords="6,186,190,229" href="#maps" alt="Contact us">
<area shape="rect" coords="7,245,189,289" href="#maps" alt="Index">
</map>

Not all images used as image maps will have null alt text. The content author must determine the most appropriate alt text for the situation.

Important

One thing to keep in mind when creating client-side image maps is that screen readers read the literal order of the HTML markup. Tools such as Dreamweaver often do not put the <area> tags next to the <img> tag. The <area> tag, which contains the alt text for the hot spots, might end up at some strange location far away from where the hot spot is viewed in the browser. This means that screen readers read the alt text completely out of context. This can be very confusing to screen reader users. If you use Dreamweaver or other similar WYSIWIG tools, be sure to look at the underlying HTML markup. If necessary, cut and paste the <area> tags to be right after the <img> tag.

Server-side image maps

Since there is no way to make server-side image maps accessible, the simplest advice is to not use them. Some people are concerned that client-side image maps cannot create the geometric shapes that they want to create, and so they use server-side image maps. The truth is that client-side image maps can make any shape at all, as long as the developer has the patience to create all of the coordinates. Below is an example of a client-side image map, with unusually-shaped hot spots, just to show that it can be done (Note: none of the links lead anywhere).

In effect, there is no reason to create a server-side image map.

Background Images

If your background image contains important text or other visual cues, you should rewrite the HTML so that the image is in the foreground so that you can apply the proper alt text.