New metadata source (re-corrected version)

[Guillaume Emont <gemont igalia com>]

Hi!

Here's another version. In that one, the test images are empty files, which
avoids copyright issues as well as bloat on the repository.
I think I addressed all of Iago's comment.

Iago: just ask if you want the micro-commits version for review purposes,
instead of this "rebase -i" version.

Guij