The "editing window" should just be the normal 3D preview, unless you are using some other preview. The regular 3D preview has controls for what aspects of rendering are enabled, Shaders (green ball), Atmosphere (blue outline of a cloud), and lighting (a yellow sun outline). Enable Shaders and you should see your image.
Hand-editing all the instances to conform to an image map may not be the best approach though, or at least not the fastest. If you can make a mask based on the satellite image, where white indicates where you want the trees to be, and black indicates where you don't, then you can simply use that as a population mask and get trees where you want them much faster. You can then edit specific trees only within the areas you wanted them in. You should be able to create such an image fairly easily in a basic image editor.
- Oshyan