Fallen said:
Design detection methods try to find the barrier between objects that can be created by natural processes and objects that can only be put together by an intelligent agent making choices.
For a fascinating dissection of that proposition I'd suggest a perusal of the following article:
What Design Looks Like | National Center for Science Education
A particularly salient point being:
In design theory, "looks designed" has been left to the imagination of the believer.
The article addresses several individual criteria by which design (or the lack thereof) may be assessed, namely; structure, simplicity, reproduction, form and function, trial and error, purpose and function, complexity-specification, functional integration, and fine tuning.
The author's conclusion (spoiler alert) is that there is actually a lot more reason to conclude that life does NOT actually fit our notion of "designed".