When you use ImageWorld it means that you can light your objects from a light, but if you just use it and do nothing else, then your object will look beautiful, but it will be floating over the image it's being lit by. Now, you could make a sphere and flip all the polygons so that they face inward and then surface that sphere as you want - ImageWorld will still work. However, that seems too much like hard work. Easier, if you just want a plain background, is to save a 10x10 pixel image in the colour you want in your favourite image editor and use the Compositing tab in the Effects window to have it as the backdrop image. Backdrop images can be of any size and they will always be resized to fill the entire background of your rendered image, so a 10x10 image will work just fine to give you a black background to your LightWave logo render...
