VolcanoCam Bug

Prompted to visit by Eric Myer’s post on the newly restored Mount St. Helens VolcanoCam, I had to laugh when this image appeared on my screen:

Screen capture of the Mt. St. Helens volcanocam image with a fly covering much of the image.

But that’s not the reason for this post. I wanted to respond to Eric’s comment that the cam image demonstrates good examples of alt text and title text. Looking at the source it seems that the designers have included the entire longdesc as both the alt and title text. I think a better example would be something along these lines:

alt="Image of Mount St. Helens, Washington USA"

title="A static image (updated every five minutes) of 
Mount St. Helens, Washington USA, taken from the Johnston 
Ridge Observatory."

And leave the longdesc as is.

Update: As has been pointed out by several commentors, the longdesc should be an URI that points to a file with the text that currently in the longdesc.

Since Eric has only enabled pings, I’m happy to host a discussion here…


I thought that longdesc was supposed to be a URL, not text…which has apparently been the problem with longdesc, as there’s no usual way to display that there is such a thing.

[goes rummaging for Joe Clark book]

ah, there we are: http://joeclark.org/book/sashay/serialization/Chapter06.html#h1-1715

yep, a longdesc is supposed to be a separate page; they’re (surprise, surprise) easy to access in Moz et al, and in later versions of Jaws, but not so much in IE.

I think it makes a rad longdesc text, it’s just in the wrong place entirely.

and I’m with you on the rest, too; it’s just a little too verbose as it is.

Posted by: Elaine on September 28, 2004 12:51 PM

I got your discussion right here. =)

I agree that the alt and title attributes on the Mt. St. Helens cam aren’t good examples. The W3C spec states that alt is supposed to be “a short description of the image.” It’s also implied (but not explict) in the spec that title is also to be used as a short descriptior. I think that Mozilla/Firefox is the only browser I know of that actually cuts off long alt/title attributes, but it still can’t be good practice to have either attribute at 255+ characters.

Additionally, longdesc is supposed to be a URI to a page further describing the image, not a string.

Posted by: Jeni on September 28, 2004 12:59 PM

I agree, 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 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 mindís eye, an analogy that holds true even for the totally blind.”

In degree of descriptiveness title is in between alt and longdesc. It adds useful information and can add flavor.

Posted by: Laura on September 28, 2004 01:02 PM

Another way to put it, is to use:

  1. The alt attribute for a short text equivalent to try to provide the same functional information that the visual user sees.

  2. The title attribute to add important or salient information.

  3. The longdesc attribute to further describe important meaning of the image.

Posted by: Laura on September 28, 2004 01:11 PM

If anything, the information that is contained (thricely!) in the alt, title, and longdesc attributes should really just be left in the content — some, if not all, of it is a duplicate of the content. Which means a screen reader user will hear it twice — that doesn’t make sense to me. Leave the alt text short, expecially when the rest of it is already in the page…

Posted by: Derek Featherstone on September 28, 2004 01:36 PM

How about sending them some nice feedback on how they should structure their img element properly?


Posted by: Eric Hodel on September 28, 2004 02:13 PM

These are all excellent points - and you’ll notice that I have updated my post to reflect the incorrect usage of longdesc.

Derek: You are right in that the longdesc text is more appropriate for the page content. In fact much of it does not really do anything to describe the image, rather it gives additional information about how the image was obtained.

Posted by: Mark Newhouse on September 28, 2004 02:19 PM

It’s excellent to see that they’ve put in some effort to at least try and make their alt text meaningful. Despite the fact that they’ve put too much in, duplicated the same text for alt, title, as well as incorrectly used longdesc, it’s still far better than the vast majority of websites that use either no alt text or worse, something like alt=”Turn images on” or alt=”spacer” (for spacer gifs, and I have seen that done!).

Posted by: Lachlan Hunt on September 28, 2004 05:34 PM

I was just writing to Eric Meyer to see if he was being facetious. Sure, any alt/title text other than “picture goes here” or “logo” or “spacer” is good, but the limitations of the two browsers I regularly use make HUGE alt text practically useless. Mozilla only displays one line of the text, and IE6/Win displays the whole thing but only for 5 seconds.

I think that the Mt St Helens example is a case of accessibility guidelines being misinterpreted by government earnestness (if alt text is good for blind people, then lets give them LOTS! Three times!). My own agency has a similarly huge and useless alt text on the home page banner (www.dot.state.ny.us). The really dumb thing is that in this case it’s a montage of five images merged into one - keeping the images separate would make for shorter, more useful alt texts.

Posted by: Dave MacEwan on September 28, 2004 07:06 PM

So, that alt text…

It’s awful.

It fails in the primary mission of alt text which is to provide a textual equivalent to the information obtained from the picture. Instead it rambles on about something unrelated which, it turns out, is in the main content just below.

The only way to provide good alt text for a picture of this kind is to put in a written description of what the picture shows. In the present case, that would probably be prohibitivly time consuming and so, the sad conclusion is, it’s practically impossible to make that page accessible to blind users. That’s not entirely unsurprising; the point of the page is to relay pictures. (That said, the text on the page might well be interesting to visually impaired users. But the webcam image itself is intrinsically visual and so very very hard to convey without visuals)

I would expect a user of an aural browser to be deeply annoyed that the page designers had conspired to waste their time so badly by including verbose, repetitive and unhelpful alt text.

Posted by: jgraham on September 29, 2004 08:21 AM

In the context of this discussion, should I be amused or saddened by the lack of alt text provided for the image on this page? Explaining the fly’s unexpected appearance would be perfect for the alt text.

Posted by: Tim on September 30, 2004 09:45 AM


Boy, there is egg on my face for this one. No excuse except that I had intended to include the alt text and in my haste to post, simply forgot. Thanks for pointing out my error, it is now fixed.

Posted by: Mark Newhouse on September 30, 2004 10:19 AM

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In which Mark starts a discussion on alt text and the like...

September 28, 2004 | web standards

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