TIFF

TIFF isn't a file format in the sense we're used to. In fact that was actually the point at the time. Dozens of vendors wanted a "standard" format but they refused to agree on anything (including even which corner of the image is the start of the image data, since all of the scanner vendors wanted to begin with whichever corner would mean least buffer RAM given their unique [probably patent-avoiding] scan order arrangements. So TIFF is a way to write metadata which enumerates all the decisions made in choosing the actual file format.

Thus there's little point trying to support "TIFF". libtiff tries but it works only for whatever TIFF formats were common enough in the wild at the time the version you have was written. Over the years there has been JPEG-encoded TIFF (early references to a 'JPEG file' are to any of the various incompatible ways to store JPEG data in a TIFF, and not to the simple JFIF standard file format eventually used today), and more recently there are numerous high-bit-per-channel TIFF variants for professional photography, most of them mutually unintelligible of course...