I started off as a German Wikipedian (where I'm a sysop and was a oversight), but now I'm a cross-wiki contributor. Beside Wikipedia, I'm an OTRS volunteer and a MediaWiki developer, though I spend little time developing these days.
I occasionally upload images or fix existing ones. Sometimes I also fix vandalism.
One image I uploaded, File:Big.Buck.Bunny.-.Frank.Rinky.Gimera.png, is featured on the German Wikipedia (although credit doesn't belong to me – I merely selected a frame from the HD version of the film for a screenshot).