xsetwallpaper —
draw an image on the root window
  
    | xsetwallpaper | [ -s] [-fcolor] file | 
The xsetwallpaper draws an image on the root window. The
  image is centered and any remaining space is filled with a solid color.
  Alternatively the image can be scaled instead.
The following options are available:
  - -fcolor
- The fill color for any margins if the image is centered. The default fill
      color is black.
- -s
- Scale the image instead of centering it.
Image formats are those supported by the STB image library. See
    http://nothings.org/stb
xsetwallpaper utility appeared in
  NetBSD 6.0.