what image manipulation libraries are in use by blender ?.

Well for my work, i have to write some image manipulation software and i usually do that in c#
But i was thinking maybe i gonna write it this time in c++ as it needs to be faster, and… well perhaps i can write something in c++ that perhaps later could be used inside blender too, if i keep it to the same image libraries. (i could for example use openCV but its not part of blender), besides i never use opencv as i usually write my own more specific & faster filters.

So with an idea of perhaps later contribute something to blender too, i was thinking perhaps a good time to get myself familiar with some dll’s. so i then might later write some filters for compositor or so.

Look at CImg.h
a offshoot of that

PLEASE do not use the mostly Microsoft ONLY c#

No was not planning for c# but for c++