Bash Script: Convert File Extension Lower Case

I wrote a small bash script for converting file extension to lower.

#!/bin/bash

PATH="/somwhere_in_the_world/"
EXTS=("jpg" "gif" "png")

for ((I=0; I<${#EXTS[@]}; ++I ))
do
  FILES=`find $PATH ! -type f -iname "*."${EXTS[$I]}`;

  for FILE in $FILES; do
    FNAME=`expr $FILE : '\(.*\)\.\w\+'`
    LOWER=$FNAME"."${EXTS[$I]}
    if [ $FILE != $LOWER ]; then
      mv $FILE $LOWER
      echo "$FILE converted to lower case.";
    fi;
  done;
done;