The Digest::TransformPath module implements the TransformPath concept.
A TransformPath is a complex higher-order key that is designed for use
with chains of functions that sequentially transform a piece of data.

The concept starts with a sizable chunk of data, for example an image,
for which we can determine a unique identifier, and for which we can
cheaply determine if and when the source material has changed. A series
of resource-intensive transforms might be applied to this original data
to produce another piece of data. In the image example, we might auto-level,
crop, scale, rotate, colour-balance and then thumbnail the image. This
transformed data would be put into a cache.  If at some future point
we wish to obtain the same image, but would preferably like to use the
cached version, we would have to take the original image, reapply the
transforms, and then compare to the result the first time around.

Further documentation is found within the module.

WWW: http://search.cpan.org/dist/Digest-TransformPath/