Image Editors
Image editing encompasses the processes of altering images, whether they are digital photographs, traditional photochemical photographs, or illustrations. Traditional analog image editing is known as photo retouching, using tools such as an airbrush to modify photographs, or editing illustrations with any traditional art medium. Graphic software programs, which can be broadly grouped into vector graphics editors, raster graphics editors, and 3D modelers, are the primary tools with which a user may manipulate, enhance, and transform images. Many image editing programs are also used to render or create computer art from scratch.
gifsicle
Tool for creating, editing, and getting information about GIF images and animations
Homepage: https://www.lcdf.org/gifsicle/
graphicsmagick++
Format-independent image processing - C++ shared library
Homepage: http://www.graphicsmagick.org/
imagemagick
Suite to create, edit, compose, or convert images in a variety of formats
Homepage: https://www.imagemagick.org/
netpbm
Toolkit for manipulation of graphic images, including conversion of images between a variety of different formats
Homepage: http://netpbm.sourceforge.net/
optipng
PNG optimizer that recompresses image files to a smaller size, without losing any information
Homepage: http://optipng.sourceforge.net/
Python
https://duckduckgo.com/?q=python+image+library
The Python Imaging Library adds image processing capabilities to your Python interpreter.
This library provides extensive file format support, an efficient internal representation, and fairly powerful image processing capabilities.
The core image library is designed for fast access to data stored in a few basic pixel formats. It should provide a solid foundation for a general image processing tool.
To install Pillow Termux
$ pkg install libjpeg-turbo
$ LDFLAGS="-L/system/lib/" CFLAGS="-I/data/data/com.termux/files/usr/include/" pip install Pillow