Sarge, my site is almost completely devoid of images (except for what design graphics came with the forum template). It's exceedingly rare when a user uploads their own and I even had extended periods of time when that functionality was either broken or disabled. So, the end result - there are almost no non-template images on a 300,000+ URLs site.
hipotecamix'es site, as far as I can tell, is almost entirely images (did I get it right, hipotecamix?). In other words, I think that seeing two extreme opposites of image usage resulting in roughly the same traffic drops on the same day, it's highly suggestive of the rather superficial role the images played in this.