I presume by "main window", you are referring to what is called the focus window (the primary workspace in Family Historian).

You are right to say that you can't open an image by clicking on the thumbnail showing to the right of the name of an individual, nor can you by clicking on any of the thumbnails in the row along the top of the focus window.

As others have indicated, if you wish to organise the images associated with an individual, click on the media tab in the property box and access them from there.  You can also view them from there.

If you only want to view the images, either for an individual or for all images in the media file, I find the easiest way is by clicking on the media button in the ribbon above the focus window, where (if you have pre-selected an individual, by clicking on that individual in the focus window) you will be given three options:  View All Media / View Pictures (etc) of... / View Media Linked to... .  Click on whichever option is appropriate and that will open the media window and display all of the thumbnails according to which option you chose.

Eric

If you have media thumbnails showing in the Media tab of the Property Box, select one then click the green circle with a right facing black arrow to display it full screen in your default viewer.

Hello to all. 

I am new, but there is one thing that feels so abnormal to me that I ask the question

Is it normal that you cannot open the media (pictures) by clicking the thumbnail right of the name of the individual  in the main windows, and that you have to go to the media menu, open the media screen, select the individual to get his media (again)
Is there no shorter way ?

thanks for your answer