Historically, ImageJ 1.x was funded internally by the Research Services branch of the National Institutes of Health. It is developed by Wayne Rasband, who is now retired, and continues his work on ImageJ1 as an NIH special volunteer.
ImageJ2 was initially funded from 2010 through 2012 by the National Institute of General Medical Sciences (NIGMS) through the American Recovery and Reinvestment Act of 2009 NIH Research and Research Infrastructure "Grand Opportunities" Grant, "Hardening" of Biomedical Informatics/Computing Software for Robustness and Dissemination. For more information on the grant call, see the listing on the NIGMS Grand Opportunity Areas page. See also the original ImageJ2 grant proposal from 2009.
The ImgLib2 project was developed by Stephan Saalfeld and Stephan Preibisch of the Tomancak lab at MPI-CBG. In recent years, ImgLib2 is funded indirectly by the various involved software efforts, including the Tomancak lab as well as the ImageJ2 project. The ImgLib2 project as a whole is organized and maintained by Tobias Pietzsch of MPI-CBG, and Curtis Rueden and Mark Hiner of UW-Madison LOCI.
SciJava is funded indirectly by the various involved software efforts, including ImageJ2, KNIME, OMERO and CellProfiler. The SciJava project as a whole is organized and maintained by Curtis Rueden and Mark Hiner of UW-Madison LOCI.
Fiji development is funded indirectly by various institutions as part of their respective research and development goals. Fiji as a whole is organized and maintained as part of the ImageJ2 effort by Curtis Rueden and Mark Hiner of UW-Madison LOCI.