TIFFReader 1.0 reads some, not all, TIFF files http://lists.squeakfoundation.org/pipermail/squeak-dev/2001-August/026468.html
This reader is written entirely in Squeak, and is thus is platform-independent, and it's integrated into the Squeak image reading and writing framework, but currently only reads 32-bit uncompressed TIFFs with alpha channels. Contains a general-purpose TIFF tag parser that could be used to pull other metainformation from TIFFs.
This is currently only available for Macintosh computers but the author John McIntosh writes: "Since all this code was BUILT for intel machines I'm SURE someone can port the plugin to Intel and Linux based distributions." (In fact the port is almost done)