It's impossible for me to upload an avatar into my profil.

Is this function disabled on Xoops.org?

You can't even pick an avatar from a list on xoops.org.

That's correct.

Because this site is such a mix of code (see the comments I've already made concerning XoopsInfo etc) - it is not possible to enable this feature.

It has previously been abused by individuals in the past - and has been fixed in 2.0.14 onwards.

However this site, for reasons of compatibility with some code used, cannot currently run on 2.0.14 upwards.

Of course, newly designed sites - such as XoopsInfo - have already had these issues dealt with... and you can freely add your own avatar on the Help forums there