i=1; 
    shopt -s nullglob;
    for f in *.jpg *.gif *.png *.jpeg *.JPG *.JPEG *.GIF; do
        EXT="${f##*.}"
        EXT=${EXT,,}
        EXT=${EXT/jpeg/jpg}
        mv -- "$f" "$i.${EXT}";
        ((i++));
    done