In the 'de' Wikipedia you can reference a piction from commons as follows:

[[Bild:Hagen Osthaus Museum Traditional Main Entrance keichwa.jpg|thumb|Osthaus Museum]]

If you click on the thumb you will be taken to:

http://de.wikipedia.org/wiki/Bild:Hagen_Osthaus_Museum_Traditional_Main_Entr...

Where you read:

This file is a shared upload and may be used by other projects.

This is not enough. Please include the description from "commons" and provide a back-link to http://commons.wikimedia.org/wiki/Image:Hagen_Osthaus_Museum_Traditional_Mai... ; [[:commons:Image:Hagen Osthaus Museum Traditional Main Entrance keichwa.jpg]] seems to do the trick. If you do not provide some such info, you don't have the right to copy the image from "commons". I release it under the conditions of the "Attribution ShareAlike 1.0 License".

IIRC, you talked about the weakness of the current system soem months ago - it is hard to believe that this rather serious issue is still not fixed.