You will avoid being biten by Unicode using binmode wherever you need to deal with a stream of bytes; from perldoc -f binmode:

               On some systems (in general, DOS and Windows-based
               systems) binmode() is necessary when you're not
               working with a text file.  For the sake of porta-
               bility it is a good idea to always use it when
               appropriate, and to never use it when it isn't
               appropriate.  Also, people can set their I/O to be
               by default UTF-8 encoded Unicode, not bytes.

               In other words: regardless of platform, use bin-
               mode() on binary data, like for example images.
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