Can you Set a picture of yours as default Ubuntu Desktop Wallpaper?

Well, setting a picture of yours as a wallpaper is totally different then setting default images as wallpaper.That picture of yours after it is deleted or moved in another location, your wallpaper either gets blank or some default images are set as wallpaper.

So in order to set your image as default image you should  work on following steps:
I have tried this tweak  on both 12.04 LTS and 14.04LTS and it works absolutely fine.
  1. First copy your image to /usr/share/backgrounds/ Do this from terminal using root prompt or do it from Nautilus  typing nautilus in terminal, so that you will not face permission denial.
  2. Edit  the XML file /usr/share/backgrounds/contents/trusty.xml and paste this code:
Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format which is both human-readable and machine-readable. It is defined by the W3C's XML 1.0 Specification[2] and by several other related specifications,[3] all of which are free open standards.[4]  (Definition referenced from Wkipedia)


Instead of Aurora_500PX.jpg keep your filename.

     3. Edit file /usr/share/gnome-background-properties/trusty-wallpapers.xml

    <name>AURORA 500PX</name>

Edit your filename instead of Aurora_500PX.jpg

Default Ubuntu Wallpapers

Look there are fourteen default wallpapers in Ubuntu. Our purpose is to set our image in that list so that next time we won't have any problem even we lose the picture or move it to another location. 

You can see the image selected with red rectangle and its thumbnail inside the monitor on your left which is the AURORA Borealis  downloaded from 500PX.com
And you can even see I have messed up with images duplication.