information on file reconstruction

I was looking for information on how to reconstruct files.
I have been looking at file systems on floppies with a hex editor and have
been trying to figure out how some of these automated programs reconstruct
deleted files or intentionally destroyed/maligned files. A friend
recently showed me how a gif file could have data intentionally inserted
into it to make it unviewable and then a program could simply reconstruct
the original photo.

Since I don't know exactly what I am looking for I'll take a guess at what
I was expecting to find.

This part of a partition tells you where known files are located. This
part of the sector tells you where the continuation of this file can be
found. This section indicates how big the file is. This symbol indicates
that the file was deleted and that it existed here.

Can someone tell me where I can find out this kind of information.

Thanks,
Philip