Normal in line image:
Retina quality (2x resolution). Will look no different than the above on normal displays but will look much more detailed on a high res display. The slight size difference comes from my smugmug site not having the image at every size.
I was reading a little on how to start supporting high resolution displays (i.e. retina displays in Apple parlance). Not easy as all solutions involve some server-side scripting that doesn't work if you use blogging services such as this site. Of course you can simply throw up high res images for everybody as I do above but that increases bandwidth for everybody.