Perhaps the previous image contained things such as parts of the craft surrounding the camera, or some kind of camera reference number. Perhaps the original images didn't have the Earth perfectly centered and filling up most of the image. They do look a lot like presentational images, not things used for scientific study, so I imagine that they tidied them up a bit so that when they were uploaded to the visitors section of the site, it didn't look all messy.
I expect it's been tampered with, but I don't see why I shouldn't trust it as an image of the planet. It's still based off of the original image, just in a cleaner version. If I wanted to some deeper investigations from it, I would probably look for the original. The continents, cloud cover and such are there, and there's no evidence of heavy manipulation on the planet itself, so I expect that NASA did the easy thing and just took a photo of the Earth.