Did you install new or upgrade from an older version?

Ty Bruno.

It's an all new installation.

Browsers up to date, and cache emptied:

Chrome at the office (Windows 7): default images OK.
Chrome at home (Windows 7): default images KO.
Firefox at the office (Windows 7): default images KO.

You help me figure that it's not pictures, but fonts that are missing. I commented Google Fonts links code because of an Ajax loading issue (in Academia theme index.php). 

    <!-- Google fonts -->
    <!--  <link href='http://fonts.googleapis.com/css?family=Merriweather&#39; rel='stylesheet' type='text/css'> -->  
    <!--  <link href='http://fonts.googleapis.com/css?family=Varela&#39; rel='stylesheet' type='text/css'>  -->  

I removed comment tags, nothing has changed. I get rid of them because it doesn't solve neither my tag autocomplete issue.

So, it's pretty clear now it's a font loading issue. How to solve it then? 

• As per iionly suggestion, turn off all third party plugins to debug. For example, right now, the academia plugin is still enabled

GET http://elgg.graphic-instinct.com/mod/academia/css/queryLoader.css 404 (Not Found)
GET http://elgg.graphic-instinct.com/mod/academia/img/slider/navigation-icon.png 404 (Not Found)
GET http://elgg.graphic-instinct.com/mod/academia/img/slider/navigation-icon.png 404 (Not Found)

• Don't know if you used an older version of .htaccess but the following is displayed when running upgrade.php

You must update your .htaccess file so that the path is injected into the GET parameter __elgg_uri (you can use install/config/htaccess.dist as a guide).

Have a look at https://elgg.org/discussion/view/1972519/upgrade-from-1819-to-197-gets-issue-you-must-update-your-htaccess-file-so-that-the-path-is-injected-into-the-get-parameter-elgg-uri

I'm using 2.1.1 elgg .htaccess version.

I don't really understand, but here is what I did: I've uploaded elgg-2.1.1\vendor\elgg\elgg\install\config\htaccess.dist in my installation folder: reloaded homepage, nothing happened. I've renamed it into .htaccess, reloaded homepage, nothing happened neither.

As per http://learn.elgg.org/en/2.0/intro/install.html#a-note-on-settings-php-and-htaccess, did you run the Elgg installer? It should have generated settings.php and .htaccess automatically. If you received an error while running it, it means you have some issues with directory or file permissions.

Yep, I did it, and everything went right at the set up: both files have been created.

I've just set up 777 the whole website installation folder and subfolders. 

In this case, go to the admin interface, turn off all the non core plugins (academia etc), clear all the server cache, try again and report whether it works or not.  

I've deactivated all plugins, and turned theme into default theme.

Settings : Advanced Settings > Caching > Use simple cache (recommended) and Use system cache (recommended) unchecked, and Save.

Nothing has changed. No font icons, no default images at home on Chrome. At the office, icons OK, but images still KO, even profile picture now. 

Activated all the bundle plugins. Profile image all right, but still no default image nor font icons at home..

The upgrade command still gives the same error, not sure why. You can turning caching off in advanced setting in admin (simple cache and system cache) and see what happens...