Este one-liner fará isso:
find path/ -name '*.jpg' -exec bash -c 'dn=$(dirname "$1"); bn=$(basename "$dn"); c=$(ls "$dn/$bn"_??.jpg 2>/dev/null | wc -l); c=$((c+1)); cnt=$(printf "%02d" $c); mv "$1" "$dn/${bn}"_$cnt.jpg' -- {} \;
Com a linha quebrada para facilitar a leitura:
find path/ -name '*.jpg' -exec bash -c '\
dn=$(dirname "$1"); bn=$(basename "$dn"); \
c=$(ls "$dn/$bn"_??.jpg 2>/dev/null | wc -l); c=$((c+1)); \
cnt=$(printf "%02d" $c); mv "$1" "$dn/${bn}"_$cnt.jpg' -- {} \;