This is a slightly manipulated version of a Hubble shot of the Lagoon Nebula. I cropped it, applied a bit selective blur to reduce the graininess and slightly changed the color curves (using gimp: http://www.gimp.org/).
I took the shot from Astronomy Picture of the Day (http://apod.nasa.gov/apod/ap101002.html).
KDE Splash: http://kde-look.org/content/show.php?content=134790
KDM Theme: http://kde-look.org/content/show.php?content=134797