This picture made from Jack - Pumpkin King (hero of "Tim Barton's Nightmare Before Cristmas" movie) with word "Halloween" repeated many-many times and coloured.
To set this picture as wallpaper you should:
1. Wait till picture will fully loaded (depending on your connection speed it could take up to few minutes)
2. Click right mouse button over the image and select "Set As Wallpaper" option
2a. If there is no "Set As Wallpaper" option on "right mouse button click over the image"
in your browser - just save this image as jpg file and use additional software or consult your system administrator ;-)