I don't upload often. Most of what I have uploaded is licensed under both CC-BY (version 4.0 as of February 2016) and the Expat license (the latter for wider license compatibility). I originally provided the three-clause BSD license as an alternative to CC-BY, but I feel that the Expat license is a better fit for non-software files due to its more general language regarding source and binaries. Some lower-quality images are covered by CC0 instead, because I don't see much of a point in retaining the copyright of low-quality images.