To cite cmtkr and the underlying CMTK library, please use:

  Rohlfing T, Maurer Jr C (2003). “Nonrigid image registration in
  shared-memory multiprocessor environments with application to brains,
  breasts, and bees.” _IEEE Transactions on Information Technology in
  Biomedicine_, *7*(1), 16-25. doi:10.1109/TITB.2003.808506
  <https://doi.org/10.1109/TITB.2003.808506>.

A BibTeX entry for LaTeX users is

  @Article{,
    title = {Nonrigid image registration in shared-memory multiprocessor environments with application to brains, breasts, and bees},
    author = {Torsten Rohlfing and Calvin R. {Maurer Jr}},
    journal = {IEEE Transactions on Information Technology in Biomedicine},
    year = {2003},
    volume = {7},
    number = {1},
    pages = {16--25},
    doi = {10.1109/TITB.2003.808506},
  }