recursively search and replace ambersands (or any character) in filenames

Replaces the ampersands with underscores in any file ending in .jpg (all subdirs)

find . -type f -iname "*.jpg" -exec rename 's/&/_/' {} \;

Same thing, but on systems that don't have 'rename' (like OS X)

find . -name '*.jpg' -type f -exec bash -c 'mv "$1" "${1/\/\&/_/}"' -- {} \;