The Devil is in the details.
The Devil is well known, super-naturally speaking, for making life difficult in many small ways. Conversely, and also from a supernatural being point-of-view, the idiom, "God is in the details," expresses the idea that whatever one does should be done thoroughly, i.e. details are important!
When it comes to photography, either phrase is appropriate. There are few things that separate a good picture from a great picture beyond those small, pesky, details reflected in the pic. READ MORE?
(Caution: Link contains an NSFW pic)