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Here is an example image without alt text:

[![enter image description here][1]][1]

enter image description here

Here is an example image with alt text:

[![Example of an image with alt text][2]][2]

Example of an image with alt text

I suspect for most readers there is no discernible difference but I believe that some users, for example those who use screen readers, will experience a difference.*

When we include images in posts, should we be adding alt text as a matter of course? If we do, what is "good" alt text - should it attempt to describe the visual appearance of the image, or simply to identify what the image is?

Moreover, should we add alt text to images on older posts, particularly on highly-viewed threads? Or is this something we should do only as part of a larger edit (e.g. fixing a typo or changing tags)? If we see that a low-rep user has made an edit request to add alt text to an image, should their edit be rejected as "Changes are either completely superfluous" or should it be approved as a potentially valuable addition? (At least, assuming that the editor is being reasonable and isn't trying to flood the front page with hundreds of such edits.)


$*$ I may be wrong but I suspect alt text might be read by search engine robots and therefore have implications for the search engine optimization of an image. This may be an additional incentive to add useful alt text, for instance if you want an image to come up as a result when a particular name of plot is searched for on an external search engine. Hopefully an SEO wizard can inform me if this is indeed the case!

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    $\begingroup$ (+1) Good points. I have always made an effort to include at least a perfunctory description of images in my posts, but I confess that in most cases they aren't terribly descriptive. But perhaps that's because I believe it's important to describe and explain one's figures in the body of the text, just to make sure readers are interpreting them as intended. $\endgroup$ – whuber Jul 25 '16 at 13:52
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    $\begingroup$ You don't need a screen reader to see the alt text; for example in Firefox, right click on the image and choose "View Image Info". The info window that pops up includes the alt text in the "Associated Text" entry. $\endgroup$ – Glen_b Jul 25 '16 at 17:04
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    $\begingroup$ This would really be more of a [feature-request] but I wish that the alt-text were used as hover-text too. That might also encourage more people to write it. $\endgroup$ – Silverfish Jul 25 '16 at 19:11
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    $\begingroup$ Perhaps also a plea for people not to use colour to make important distinctions in their graphs as people with colour vision anomalies have difficulty with this. $\endgroup$ – mdewey Jul 25 '16 at 19:36
  • $\begingroup$ Honestly, I almost never include alt text but almost always describe what in going on the plot in the body of my answer - is there any problem with such approach? $\endgroup$ – Tim Jul 29 '16 at 9:03
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    $\begingroup$ @Tim Anyone using a screen reader gets a dose of "Enter image description here" which must be a bit annoying, particularly if there are several images. Even cutting this down to "Plot" would be an improvement, I'd imagine $\endgroup$ – Silverfish Jul 29 '16 at 10:45
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Given that we have at least a few vision-impaired readers who have mentioned this fact on our site (and no doubt many more who don't post or don't mention it), I think we should attempt to add at least brief alt text as a matter of course -- it's just a matter of replacing "enter image description here" with a description of the image. Even a brief one-sentence description is better than none, though longer descriptions are better still. Alternatively, describe it in the text of the post.

As for what to do with old posts I certainly suggest adding a description if you happen to be editing a post, but I wouldn't necessarily start a wholesale rewrite of old posts because we would bump thousands of posts. We should really only bump a few a day, so it would be years.

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