The guitar pictures are distributed under the Creative Commons Attribution ShareAlike 2.0 Germany License since they derive of the following work: 

guitar: 
    creator: Martin Moeller
       name: Classical_Guitar_two_views
    licence: Creative Commons Attribution ShareAlike 2.0 Germany License
             (http://creativecommons.org/licenses/by-sa/2.0/de/)
       link: http://de.wikipedia.org/wiki/Bild:Classical_Guitar_two_views.jpg
	

The drumkit pictures are distributed under the GNU Free Documentation License since they derive of the following work: 

drumkit: 
    creator: Clngre 
       name: Illustration of a drum kit for "drum kit component" 
    licence: GNU-Lizenz für freie Dokumentation 
             (http://commons.wikimedia.org/wiki/Commons:GNU_Free_Documentation_License)
   found at: http://de.wikipedia.org/wiki/Bild:Drum_kit_illustration_template.png