Ken,
What I do on my computer is resize the original to 72 dpi and either 764 or 1000 pixels on the wide side. That should be enough to get good results. I save them as a copy, that way it doesn't effect the original. All the photo sites have different compression and will sometimes mess with color or cropping a little. I don't mess with that, I leave it like it is. It is frustrating I know.
