add Licence during user submission of cover picture

[BenjMy]

During the user online submission form:

• add a statement saying that the cover picture must not be protected by copyright.
• ask the user contributor to choose a Licence and insert a copy of the appropriate icon/text statement below the picture.

Possible licences:

• Licence Creative Commons
• ...

[sagitta1618]

I'd rather state that any cover picture uploaded must be free of copyright (and will be placed under a creative common licence - like on wikipedia).