If you look at the top selling 3D pictures of a microstock site, you will notice that some of them are just plain Earth globe pictures. This is a relic from the early days of microstock, where agencies had to build up their stocks and were eager to accept just about any picture that met a minimum quality standard.
Today, none of the major agencies will accept such pictures anymore. As most of the imagery is based on NASA pictures, they don’t want you to make money just by copying a plain picture. And they are right, in my opinion.
But with some creativity you still can create pictures that will get accepted and will be sold. Projecting the picture onto unusual objects is always a good place to start. Or try to put Earth into unusual situations or an everyday scene where it can replace something round. And if you can give it a symbolic meaning as well, even better.
Earth is a timeless subject. The things you can do with it in microstock graphics are only limited by your own imagination.
