I have a Wordpress upload folder that is structured using subfolders for months.
wolfr2:uploads wolfr$ tree . . |-- 2007 | |-- 08 | | |-- beautifulkatamari
This will copy all *.jpg files from the current folder to a new folder and preserve the directory structure.
tar cvfp `find . -name "*.jpg"` | (cd ; tar xfp -)
To copy without preserving the directory structure:
cp `find . -name "*.jpg"`