HTMLImageElement.longDesc

The obsolete property longDesc on the HTMLImageElement interface specifies the URL of a text or HTML file which contains a long-form description of the image. This can be used to provide optional added details beyond the short description provided in the title attribute.

descURL = htmlImageElement.longDesc;
htmlImageElement.longDesc = descURL;

A DOMString which may be either an empty string (indicating that no long description is available) or the URL of a file containing a long form description of the image's contents.

For example, if the image is a PNG of a flowchart. The longDesc property could be used to provide an explanation of the flow of control represented by the chart, using only text. This can be used by readers both as an explanation, but also as a substitute for visually-impaired users.

This property is obsolete and should no longer be used. Instead of using longDesc to provide a link to a detailed description of an image, encapsulate the image within a link using the <a> element.

Consider the following older HTML:

<img src="taco-tuesday.jpg" longDesc="image-descriptions/taco-tuesday.html">

Here, the longDesc is used to indicate that the user should be able to access a detailed description of the image taco-tuesday.jpg in the HTML file image-descriptions/taco-tuesday.html.

This can be easily converted into modern HTML:

<a href="image-descriptions/taco-tuesday.html">
  <img src="taco-tuesday.jpg">
</a>

With that, the image is a link to the HTML file describing the image in more detail.