I've solved this with

davecoventry — Sun, 26 Jul 2009 07:20:49 +0000

I've solved this with another dreadful hack.

I've created a new table: drup_picture_files with fields name, type, path.

I've created the new directory sites/default/files/picture/users/username

I've use file_save_upload to allow the user to upload the file

I've added the user name, type and path to the drup_picture_files table.

And for the avatar, I've used a SQL UPDATE to set the user's picture field to the sites/default/files/picture/users/username directory. Seems to work.