[CentOS] recursively find duplicate filenames

Wed Jan 5 11:15:03 UTC 2011
S Mathias <smathias1972 at yahoo.com>

find duplicate filenames in a folder
find | perl -ne 's!([^/]+)$!lc $1!e; print if 1 == $seen{$_}++'

find duplicate filenames in a folder recursively
? how?