1. Find the size of the image ie (800x600)
2. Create a plane with the same dimentions as the image.
3. Open the material editor and asign the image to a material slot.
4. Asign the materal to the plane.
Dont change the material type, leaving it on standerd is fine. Have a look at the image i have attached. Select the small gray box next to where it says defuse and then select bitmap, from here a brower window appears and you select the image. You will see the image over one of the sphears rather then a flat image. Make sure you check show map in view port (also shown in the image) and then assign it to your object. I recomend using a plane insted of a box as the primitive as it does not have a back or sides, the box will have the image on both sides.