RE: WA - background-image in CSS

you said
Therefore, I could use the CSS background property for the inclusion of ALL
non-essential elements, and then I would not have to use the "alt" tag.  A
blind user gets the same ESSENTIAL CONTENT as the user who can see the page.

This was not just refering to the background image but ALL that YOU consider
non essential.

Charles said a bacground image must not contain essential information, I do
not think he said that other information can be hidden this way for a class
of user.

Harry Woodrow

-----Original Message-----
From: []On
Behalf Of RUST Randal
Sent: Friday, 18 January 2002 10:59 PM
Subject: RE: WA - background-image in CSS


If I have an image that I, as the author of the page, deem does NOT CONVEY
CRITICAL INFORMATION, such as a picture of trees, then I SHOULD FEEL FREE TO
OBVIOUSLY I will include it in the HTML, and properly apply the necessary
attributes for accessibility.

That what I said in my very first post.

-----Original Message-----
From: Charles McCathieNevile []
Sent: Friday, January 18, 2002 9:37 AM
To: Access Systems
Subject: Re: WA - background-image in CSS

Well, there are two ways of looking at this.

On one side, it is important for accessibility to convey the essential
information - a page often contains lots of supplementary stuff to highlight
and reinforce its message(s), and a user can find out those are there and
look them up if they have an appropriate browser. In some cases part of that
information will be in an inaccessible form. In the real world there is then
a tension between whether someone provides more new information that they
consider it important to convey, or whether they render existing information
more accessible.

In order to meet WCAG, there is a requirement that the background image (as
part of the style) not convey critical information that is not otherwise
available. That requirement makes sense. In text form, alt="" (in otherwords
a null statement) is therefore an acceptable equivalent, for the purpose of
meeting checkpoint 1.1. In fact with the background image there is no easy
wayt to include alt information, or a description. That doesn't mean there
no way of doing it at all.

If people are aware of how the Web works well - i.e. things don't appear in
multiple places, they have an identifier (URI) that can be used to find
and local services can cache the content of that identifier for speed or
offline work (browsers do this automatically to a large extent, and there
ways of doing it on a wider scale), there is more that can be done.

It is possible to find out what the background image is - at worst by
inspecting source, although some browsers give direct access, and more tools
could be made that do so - at least as far as having a URI to be ableto look
at it.

Then all that is required is that there is a way of getting information
the image. Some approaches from W3C spring to mind...


Annotea is a service that allows anyone to annotate anything with a URI - a
page, part of a page, an image, an image as used in a particular page, etc.
The annotation can be anything else on the Web - another page, a bit of text
written for it, another image, and it has a type - comment, example, test,
seeAlso, ...

There are tools to use this in Amaya, Mozilla, Internet explorer, any
javascript capable browser. It is also possible to do it from
non-script-capable browsers via a Web interface. Details of Annotea are at


RDFPic is an example of a tool that incorporates information directly in an
image - the open source demo tool does it for jpeg images, and allows you to
save the image (using HTTP PUT - a standard that is sadly still not
widely-enough implemented) including the information. The Jigsaw server (for
which the demo was written) allows you to retrieve the information instead
the image, or it can be extracted from the image itself with a bit of a
More about RDFPic at which includes links to
online demos


A lot of browsers don't yet handle SVG. On the other hand we are only
about a background image, so that may not trouble some people. In SVG
including a descriptionis trivial - consider the following two images:

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
<svg width="100%" height="100%"   xmlns="">
  <desc>A washed out background colour with spots on it</desc>
  <image xlink:href="" width="100%"

(which shows how to use a bitmap image within an SVG)


<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 20010904//EN"
<svg width="8cm" height="4cm" viewBox="0 0 800 400"
  <desc>A colour gradient - red on the left blending to yellow on the
      <linearGradient id="MyGradient">
        <stop offset="5%" stop-color="#F60" />
        <stop offset="95%" stop-color="#FF6" />
    <rect fill="url(#MyGradient)" width="800" height="400"/>

Which is a complete image in itself - compressed this uses a very small
number of bytes indeed.

Both images above include a description, which can be easily extracted.

There are other image annotation systems available of course, which can do
the same kinds of things as RDFPic or annotea via a Web Query: as an example
see (an
implementation designed for collecting pictures of multiple people, and thus
finding out who has been in the same place as whom, ...)



On Fri, 18 Jan 2002, Access Systems wrote:

  On Fri, 18 Jan 2002, RUST Randal wrote:

  my opinion only ! (well maybe not just me but I do not speak for others)

  > blind user gets the same ESSENTIAL CONTENT as the user who can see the

  users with disabilities or other reasons for using alternative screen
    DESERVE AND ARE ENTITLED TO ALL THE CONTENT, who are "you" to determine
  what is "essential" content to me

  THIS IS ONE of the major complaints of almost all people with disabilities
  in all areas of access.  NO ONE!, period, has the right to determine my
  needs and priorities.

  *you and me as used is generic and not intended to mean any one individual
  ** really one of my major peeves!
  *** shouting is intentional and needed

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Charles McCathieNevile  phone: +61 409
134 136
W3C Web Accessibility Initiative    fax: +1 617
258 5999
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(or W3C INRIA, Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex,

Received on Friday, 18 January 2002 10:04:48 UTC