Why both gThumb and F-Spot are in Ubuntu?

You can remove the one you don't like if you want. gthumb is considered an integral part of the gnome desktop, so if you remove it you will also remove the ubuntu-desktop package. This is not a real problem however as this is just a meta package.
Note however that these packages are meant for two different purposes:

gthumb is mainly a thumbnail viewer (it is for instance used to view your images as thumbnails when using Nautilus).
F-spot is more meant to be a photo management application.

Thanks for your answer, but I don't know if projects which are related in http://www.gnome.org/projects/ are just hosted by gnome.org, or if they are official projects.

Because I thought it's the opposite stuff : F-Spot, a part of GNOME, and gThumb, a depend of meta-package ubuntu-desktop.

Can you answer to my question about gnome projects, and confirm that gThumb is not obsoleted ?

Jonathan, this is a technical support service, it is not the place to discuss policies.

You question was:

Why gThumb *AND* F-Spot are both in Ubuntu

And my answer was very clear.

If you want to know what Gnome officialy supports or not supports, you'd better be off asking Gnome.

Thanks Cesare Tirabassi, that solved my question.

Solved => Re-Opened :

 I have got more informations, and I believe that you confused gThumb and EOG, after to take a look on Internet, the conclusion is clear: gThumb and F-Spot make the same functions with some exceptions, therefore, I re-open my question.

Jonathan, it's still no technical issue.

So I kindly ask you to be considerate and discuss these issues at http://ubuntuforums.org. You might also file a feature request at the bugtracker or start a blueprint.

The technical issue tracker is just the wrong place to discuss policies.