Adding OS X Icons
Simplify image management by storing your Mac OS X icons in an asset catalog.
In the project navigator, select an asset catalog.
Choose Editor > New OS X Icon.
An empty OS X icon set is created, with an image well for each image representation in the set.
In the Finder, select an icon file and drag it to the appropriate image well in the set viewer.
Alternatively, you can add images by choosing Editor > Import.