Install Line Deco app to download the wallpapers. GD's was released today, Taeyang's will be released tomorrow, and the shared photos with both of them will be released the 27th.
Please note that unfortunately this feature does not seem to be available in the German download. If you experience similar difficulties, please let us know.
Wallpapers below:
Source: Line Deco via @TeamBigBang and @bigbangupdates