It would be helpful to add a Webcam example that is in accord with WCAG2 to the
"HTML5: Techniques for providing useful text alternatives" document:
http://dev.w3.org/html5/alt-techniques/

The Current HTML5 Editor's draft currently states:

<q cite="http://dev.w3.org/html5/spec/text-level-semantics.html#unknown-images>

In some unfortunate cases, there might be no alternative text available at all, either because the image is obtained in some automated fashion without any associated alternative text (e.g. a Webcam), or because the page is being generated by a script using user-provided images where the user did not provide suitable or usable alternative text (e.g. photograph sharing sites), or because the author does not himself know what the images represent (e.g. a blind photographer sharing an image on his blog).

In such cases, the alt attribute's value may be omitted, but one of the following conditions must be met as well:

* The title attribute is present and has a non-empty value.
* The img element is in a figure element that contains a figcaption element that contains content other than inter-element whitespace.
* The img element is part of the only paragraph directly in its section, and is the only img element without an alt attribute in its section, and its section has an associated heading."
</q>

Thank you.