The authenticity of a documentary is ‘deeply linked to notions of realism and the idea that documentary images are linked to notions of realism and the idea that documentary images bear evidence of events that actually happened, by virtue of the indexical relationship between image and reality’
Horness Roe. A. (2013) Animated Documentary. Basingstoke: Palgrave Macmillan.
The authenticity of the documentary is demonstrated by
A documentary film is a non-fictional motion picture intended to ‘document reality’.
And the concept of realism is ‘Realism in the arts is generally the attempt to represent subject matter truthfully, without artificiality and avoiding speculative fiction and supernatural elements’.
Both are based on real events, without adding fictional elements and avoiding modifications that contradict the truth.
Also, Documentaries convey information by restoring images of realistic scenes and providing evidence of the actual events that took place.