Attribution when creating images from other sources
I think it's somewhat unusual for academic papers to have a Credits (I would use the plural) or Picture credits, for two reasons:


Academics usually strive to produce their own content, rather than reuse.
Most people wouldn't follow the proper attribution/disclaimer rules.


I, however, think your way of doing things is very adequate. Your Creative Commons attribution seems correct: as you can see here and there, the CC attribution requirements are actually pretty flexible.



The one thing I might do differently is the use of references for each of the attributions. It seems a bit overkill (takes up more space) and somewhat blurs the purpose of the references list. I would simply put the attributions inline in the text:


  This diagram also utilises the following third party images: server (by mimooh, 12-Aug-2011, http://openclipart.org/detail/155101/server-by-saisyukusanagi), etc.


Also note that, at least for openclipart.org but also for other online resources, you can actually abbreviate the URL without loss of functionality: http://openclipart.org/detail/155101 instead of http://openclipart.org/detail/155101/server-by-saisyukusanagi.