TIFF is an acronym for Tagged Image File Format - a format for storing image data. See http://www.libtiff.org/ for the source code.
See Image, Img, Photo format - HPL (Fitzhugh), and QuickTimeTcl for some Tk extensions which support TIFF. See also tiff package (in pure tcl), Xbit and tcllib.
ZLM: this is my summary of what each package provides. Authors, please correct me. Who wrote tiff package (in pure tcl) anyway?
tiff package (in pure tcl) - this allows creating Tk image (type photo) objects from TIFF images (compression modes supported: Uncompressed, CCITT 1D, Group 3 Fax, Group 4 Fax, LZW, JPEG or PackBits.) ; saving uncompressed RGB TIFF files.
img extends the existing Tk command image so that it supports TIFF files. Can write compressed files (compression modes: uncompressed, jpeg, packbits, or deflate). Contains the package tifftcl, which is a Tcl wrapper around the TIFF C library.
Xbit also supports multi-image files.
tcllib tiff - read and write image metadata such as size and comments, read and write uncompressed images.