Or, better yet, don't create a global pointer because you don't need it. Just call DXUTGetD3D9Device whereever you need the pointer. For example:
createScreenshot(DXUTGetD3D9Device());
That will ensure that you get a pointer and eliminate any confusion with local/global variables, etc.
You definitely don't need to call DXUTGetD3D9Device inside the CreateDevice callback, since the framework passes the device pointer in the first parameter.