The CImg Library is an open-source C++ toolkit for image processing.

It mainly consists in a (big) single header file CImg.h providing a
set of C++ classes and functions that can be used in your own sources,
to load/save, manage/process and display generic images. It's actually
a very simple toolkit for coding image processing stuffs in C++ : Just
include the header file CImg.h, and you are ready to handle images in
your C++ programs.

Note: The archives hosted on http://cimg.eu/files/
do not contain the HTML documentation.  Please refer to
http://cimg.eu/reference/index.html or download a copy from
https://github.com/dtschump/CImg