Version 1.10 of DEM Earth or later has an Image Download Extension built into it. This premium feature gives you a one click downloading solution and gives access to many web based image overlays.Many of these layers are open source based, but you should always check with the respective copyright holders for comercial usage.
You can use any imagery with DEM Earth. Here is a short list of some of the major *Sat Image Providers, where you can license and purchase sat images.
There are too many to list here, and there is usually an agency that resells for the major content providers, in each country.
* Be sure to purchase images with a world file, WGS84 and in geographic coordinates, so you can easily georeference it in DEM Earth.
If you have the skills you can use something like Global Mapper (PC only) or ArcGIS (PC only) to reproject any sat image to work with DEM Earth.
To make life easier, you want to obtain images with a world file for
referencing and that world file needs to be in geographical coordinates, (not UTM). Datum should be WGS84.
If you are using Mercator images (Google & co) for large areas you will need to re-project from Mercator to Geographic (WGS84) then everything will fit perfectly.
Get in touch if you have no idea how to re-project images and I can do it for you.