The image is simply a screenshot of an excerpt of something Laura Carlson said in public-html-a11y@w3.org on the 24th of August 2010

I could have provided the transcript of what she said here. However, the purpose of a longdesc link — according to what Laura said (and she also quoted from a WCAG document) — is not specifically to provide non-graphic versions (rel="alternate") of a graphic, but to provide a longer description of what the image tells. The transcript of what Laura said is in this case — anyway — available via the @cite attribute link of the q element that encapsulates the img element.

Thus, for intstance CSSsquirrel’s use of the longdesc attribute in his ridiculously funny — and telling! —  Comic #72, is thus perhaps not entirely “correct”, as it provides a transcript ... rather than a description of what the image tells ... Well. It depends. Irony and wit turns upside down on everything.

So the the longdesc text you are reading right in this moment ... can be justifed as an ‘high-level’ indept description (though not, in the most literal sense, of course ...) of the image — and thus is a ‘valid’ longdesc ...

Ironic afterwords: A sighted user of course did not need to read this text ... he or she could just look at the image and ... think there were nothing more.