A couple other things to consider. At the bottom of the planes properties in the channel box you will see create UV's as a matter of practice I change this to "normalization off" you then have to be sure the aspect ratio of the plane you create is correct.

To ensure the plane you creates aspect ratio is correct look at the dimensions of the image. I use adobe bridge which shows me both the pixel and inch resolution of the image. I prefer to use the inch dimensions. If the image is say 10.9 inches by 7.7 inches I create a plane that has width 10.9 and height 7.7. When the shader is applied the image will be stretched to fill the entire plane and will have the correct aspect ratio.

If you choose the last option "normalize and maintain aspect ratio" the image will fill the entire plane but may be clipped if the plane is not oriented properly or created with the proper aspect ratio.

I have found no use for the "off" option.