I have a Wordpress upload folder that is structured using subfolders for months.
wolfr2:uploads wolfr$ tree . . |-- 2007 | |-- 08 | | |-- beautifulkatamari
Off the top of my head:
find . -type f -name \*.jpg -exec cp \{\} $TARGETFOLDER \;
If that doesn't work, comment and I'll try again, but find is definitely the way to go.
find