Detect real character set

Is there any way to detect the real character set use in columns? I've
just seen a mysql 4.0 database where the default character set was
latin1 but greek was being inserted. When that database was upgraded to
4.1 the greek became unreadable. So I guess I'm asking how can I detect
this so I can run a process on suspected databases and ALTER them to
the correct character set.

Thank you,

Robert Boone