most movie have used visual effects to recreate dragons/dinosaurs and some for animals and even some locations, backgrounds.
such as game if thrones most of the show is visual effects, you can’t actually have large and small dragons so they had to make a head of on a stick and then wrap it in green felt from a green screen. Then use some visual effects on the head on a stick to make it seem as if their is a dragon actually there. 
Another movie that used visual effects to create massive motorways that would normally have had to been closed of and that would cost a load of money as well would the cars being trashed and destroyed.
the difference between blue screen and green screen are they both are used for background but the difference is the colour because if the blue screen is used it might make the colour of the sky different since it might be the same colour of the sky. so many film makers are using green screen more often so that the dont have to worry about that mistake happening when they’re outside using it
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