If you need to insert the image for lighting (an HDRI image to light the scene), you can replace the default Environment node connected to the Scene node, with an HDRI node. Just select and delete (press Del) the Environment node, and right-click over the environment connector on top of the Scene node, and select Add-Connect to a new-HDRI Environment.
Then right-click over the dark grey background and Add-Textures-Image texture from file, import the image you want, and connect its node to the Map connector (not sure if that is its proper name) node. The image will be added and will be lighting the scene. You can then tweak its parameters on the upper panel.
Here is a screenshot showing how it looks with the new nodes:
Hope that helps!