Attribution. Images marked with this sign may be copied, distributed, and displayed — and derivative works based upon it — but only if credits are given the way the copyright holder specifies.
Share Alike. Others are allowed to distribute derivative works only under an identical license.
This license lets others remix, tweak, and build upon the original image even for commercial reasons, as long as they credit the copyright holder and license their new creations under the identical terms. This license is often compared to open source software licenses. All new works based the images will carry the same license,
so any derivatives will also allow commercial use.