Development of ImageResizer is funded by our commerical licences to the Performance and Elite editions. Commercial licenses also include source code and permit modification; most permit redistribution.
All Imazen software is open-source, and your funds help (both directly, and indirectly) maintain dozens of critical low-level, permissively-licensed OSS libraries across a wide spectrum. Visit our GitHub profile to see some of the work we maintian.
If you are able to comply with the AGPL v3 and provide the public with access to the complete source code for your website/service under any AGPL v3 acceptable terms (which includes MIT, GPLv3, and Apache 2), then you may use all ImageResizer plugins for free under the terms of the AGPL v3.
Looking for version-specific licenses? They can be found here, but will shortly be discontinued.