Thanks for the reply, Gus. I just found this posted on the 25th on the Paint.net forum when I went-a-searchin'...
Random guy asks: "First let me say that Paint.NET is mind-bogglingly good. It blows me away.
Having said that, it is astonishing that it does not have a crop feature that includes the common photo cropping aspect ratios (e.g., 4x6, 5x7, 8x10, etc.)
It is literally -- and I mean "literally" literally -- the first thing I tried to do with the program.
It arguably the most basic task to be performed on a digital photo to prepare it for printing, and un-arguably in the top three.
The workarounds posted in this forum are woefully convoluted and inadequate for what should be a very simple task."
Product lead developer responds: "This is one of the top feature requests and something we're looking to implement in an upcoming update."
I'm going to go out on a limb and say little IrfanView doesn't have it, either. I did read a comment about it being part of Picasa, though. I guess that means I'll be downloading another program for the task... but hey, I'm glad you alerted me to this one-step capability! Now imagine plodding along with your F20 for over six months without knowing about it. ;-)