I wonder if anyone has noticed this up to now. I only happen to catch this during the last OS X update 2013 003. I happened to be staring at the screen as my machine installed the update and displayed the linen background. I was focusing to a point beyond the screen and realized that the linen background is in fact a stereogram. Kind of neat. Not useful by any means but cool to look at. I immediately changed my desktop background to the linen background to confirm and sure enough, it's a stereogram. When you stare at it just right, you see it pop out just like the well known stereogram pictures. I googled it and saw no reference to this anywhere. Just though I'd ask if anyone had noticed this already and if anyone could confirm. Just a side note however, the linen background displayed during the update is lighter than the one you can set as a desktop background. I found the lighter one to be easier to see than the darker one.