People view your image by clicking on the thumb. so you have to put the best part of your image in that thumbnail.

Also some people don't like it when you create a image using other peoples meshes (like the ones from 3D Cafe). Some even consider it Lazyness. Maybe next time you should create your own meshes and get more viewings... And than again: getting fewer viewings doesn't mean that you created a bad image, It just means that people maybe don't like it. and that's a difference...

About the gamma correction: If you are a regular Bryce user you should know where to find it: It's one of the little green triangles next to the render and camera tools It's the lower-most one, right next to and below the trackball. Hope this will help you....