Another analogy that came to me the other day was the "Face" on Mars. Using the design inference, we would have to come to the conclusion that an intelligence put this structure on Mars. However, using a naturalistic viewpoint, the "Face" can be explained as combination of chance erosion and shadows that the human brain construes as a human face.
Another example is the difficulty archealogists have in determining whether a tool find is actually an artifact or a naturally chiselled rock. IOW, the definition of design can be tenuous. What appears to be natural may in fact be designed. How does ID differentiate between the two? ID postulates an intelligent designer using man-made or humanly identifyable objects as evidence. If a scientist can't tell me whether the object in my hand is a stone axe or a rock, how can ID tell me life is the product of god?