Yea i know what you mean you try paste it on paint and its black , no image.
Instead try this.
In game press "P" key to take an image whilst playing or watching a replay.
Then after ur done , go to your Aeriagames folder , Soldier front , Data , Screenshots.
Picture will be in there.
Note : you can press P as many times as u want ingame as it saves instantly when you press P.
so yes , you could take more then one , without having to save it , since it saves itself.
Hope that helps o.O