Fixed by changing the schema to add a default value of zero.

This value is always directly changed by Ansel_Faces code, and never 
by the Ansel_Image class, so writing it in Ansel_Image#save results in 
wasted resources.

Thanks for the catch, though :)

Changes have been made in CVS for this ticket:

[mjr] Fix default value for image_faces value in the database schema 
(Bug #8925)
http://cvs.horde.org/diff.php/ansel/docs/CHANGES?rt=horde&r1=1.61.2.32&r2=1.61.2.33&ty=u
http://cvs.horde.org/diff.php/ansel/lib/Ansel.php?rt=horde&r1=1.517.2.75&r2=1.517.2.76&ty=u
http://cvs.horde.org/diff.php/ansel/scripts/sql/ansel.pgsql.sql?rt=horde&r1=1.5.2.8&r2=1.5.2.9&ty=u
http://cvs.horde.org/diff.php/ansel/scripts/sql/ansel.sql?rt=horde&r1=1.29.2.10&r2=1.29.2.11&ty=u
http://cvs.horde.org/co.php/ansel/scripts/upgrades/Attic/2010-03-24_fix_default_faces_value.sql?rt=horde&r=1.1.2.1

When using database backend, ansel defines 'image_faces' on 
'ansel_images' table as not null (ansel/scripts/sql/ansel.sql), but it 
is missing at lib/Ansel.php 'save' function. It results in errors when 
inserting a new image.

Something like the attached patch solves the problem.