Answer by Nasreddine for easy way to automatically retrieve image for desktop background?

Yes. you can for example use NASA's image of the day rss feed as a wallpaper (it will download the new image automatically). Just copy/paste this in plain text file with the .theme extension :

[Theme]DisplayName=Nasa[Slideshow]Interval=1800000Shuffle=1RssFeed=http://www.nasa.gov/rss/lg_image_of_the_day.rss[Control Panel\Desktop]TileWallpaper=0WallpaperStyle=0Pattern=[Control Panel\Cursors]AppStarting=%SystemRoot%\cursors\aero_working.aniArrow=%SystemRoot%\cursors\aero_arrow.curCrosshair=Hand=%SystemRoot%\cursors\aero_link.curHelp=%SystemRoot%\cursors\aero_helpsel.curIBeam=No=%SystemRoot%\cursors\aero_unavail.curNWPen=%SystemRoot%\cursors\aero_pen.curSizeAll=%SystemRoot%\cursors\aero_move.curSizeNESW=%SystemRoot%\cursors\aero_nesw.curSizeNS=%SystemRoot%\cursors\aero_ns.curSizeNWSE=%SystemRoot%\cursors\aero_nwse.curSizeWE=%SystemRoot%\cursors\aero_ew.curUpArrow=%SystemRoot%\cursors\aero_up.curWait=%SystemRoot%\cursors\aero_busy.aniDefaultValue=Windows AeroLink=[VisualStyles]Path=%SystemRoot%\resources\themes\Aero\Aero.msstylesColorStyle=NormalColorSize=NormalSizeColorizationColor=0X6B74B8FCTransparency=1[MasterThemeSelector]MTSM=DABJDKT

as you can see here the interesting line is

RssFeed=http://www.nasa.gov/rss/lg_image_of_the_day.rss

you can use any RSS feed you want.

Reference