The CImg Library provides a minimal set of C++ classes that can be used to perform common operations on generic 2D/3D images. It is simple-to-use, efficient, and portable. It's a really pleasant toolkit for developing image processing stuffs in C++.
A simple version of the Jawbreaker game, made with CImg
Fourier filtering demo, part of the main CImg sample program
A simple 2D blobs editor, made with the CImg Library
Example of CImg plot capabilities
A 3D viewer of DT-MRI images, with fibertracking.
Demo menu of the main CImg sample program