It means simply that I do not want you to have a transparent background or whatever. You will have to design a background for the subject. Or, make it all purple I dont care, but that would look stupid.
Changing opacity would be cheating, also. I would rather you are able to convey the appearance of the object being semi-transparent without doing that automatically...but I dont know if I would be able to accurately keep that under check or not so...I guess your on the honor system there.
Edit:
Dang, re-reading through the initial post, I found a couple errors and I realized I forgot a rule. I originally was going to end the contest on the 4th, and I reconsidered that and changed it to the thirth (3th) X__X
Be sure to re-read that first post after a 10th rule is added.