September 2004, Version 0.7.0
Added readonly support for shared thumbnail repositories
September 2002, Version 0.6.1
The subdirectories weren't a good idea. Removed them from this version.
Updated link to the MD5 implementation.
September 2002, Version 0.6
Added another sub directory level within the cache base directories to avoid too much clutter.
State not to create thumbnails for files within the thumbnail cache directory.
State when it's allowed to use thumbnails which haven't been checked for validity.
Some typo fixes.
Introduction and conclusion rewrite.
Janurary 2002, Version 0.5
Changed handling of different thumbnail sizes.
Propose using temporary filenames to avoid problems with concurrent access.
Save thumbnails directly in the size dir without subdirs.
Added optional Thumb::Mimetype key
Give some more implementation notes.
Added "Thanks" section.
December 2001, Version 0.4
Destinction between required and optional thumbnail attributes.
Dropped distinction between global/local .thumbnail directories.
Use MD5 hashes as thumbnail filename.
Initial attempt to handle concurrent accesses by different programs.
Rewrote the "Deleting Thumbnails" section.
August 2001, Version 0.3
Rewrote this paper.
July 2001, Version 0.2
Removed distinction between low/high quality thumbnails.
Seperate directory for failures.
Consider permission settings.
July 2001, Version 0.1
First public release.