My suggestion is LDAP.....................

There is no "best" way. It depends on your requirements.

How many pictures will there be? Can they be easily organized into
folders / directories?

Does your database  support BLOBs? Do you already have connectivity to a
database?

I'm using spring, hibernate and mysql, so the database  supports blob.
the problem is I don't have enough experience in designing project architectures like this.
the result is supposed to look like something similar to yahoo photos page.
users login, create/edit photo  albums. share them with others.
I don't know if using database for such projects is a routine task.

Another important factor, although it is not
technical, is the size of the database. If you want to
(or it is likely to) deploy your application  on a host
with limited database  size, it is reasonabale not to
waist your database space.
As you may know, Orkut (unlike yahoo photo  album)
saves the pictures in the folders.