how do i make the background an image instead of the blue screen
You either texture map a plane, set it shadeless so the lights don’t affect it and then position and scale to suit.
You go to the materials buttons, then click the blue circle icon (World Buttons).
Add a new texture on the right, click the “map to” tab and select “Hori”
switch to the texture buttons and tell blender that you want to use an image for this texture and where that image is.
The second option will affect the color of your scene when using YafRay. This is how you incorporate images into the lighting and reflection calculations of cars, for example.
You can look up HDRI with blender for more info.