It's easier to see issues on white surfaces. He could have taken it of something else but it's harder for the untrained eye to see errors unless it is pointed out. The capture is clearly for diagnosis purposes... talk about not thinking.
I think it's spelled R-E-L-I-E-F. I experienced a lot if it myself when mine turned out to be okay. Haven't taken any pictures of plain white stuff yet, though. Regular old photos come out great. I think that'll do.