libdlib-dev 18.18-2build1 (amd64 binary) in ubuntu bionic

 Dlib is a general purpose cross-platform open source software library written
 in the C++ programming language. It now contains software components for
 dealing with networking, threads, graphical interfaces, complex data
 structures, linear algebra, statistical machine learning, image processing,
 data mining, XML and text parsing, numerical optimization, Bayesian networks,
 and numerous other tasks.
 .
 This package contains the development headers.