What is ImageJ?
ImageJ is an open source image processing program for multidimensional image data, with a focus on scientific imaging.
What can ImageJ do?
ImageJ provides a wealth of image processing techniques, including colocalization, deconvolution, registration, segmentation, tracking, visualization and much more.
ImageJ is supremely extensible, with thousands of plugins available which provide additional features via update sites, written by members of a diverse community.
How do I get started?
Get ImageJ from the Downloads page. Then peruse the User Guide and Tutorials.