According to me, the easiest way to describe authenticity is that, authenticity is something that is genuine, not replicated or plagiarized. In terms of art, I do not believe that it is possible to be truly authentic. There are various artists who usually use ideas and concepts of other artists and try to replicate the design with a twist of their own and some also try to something that is more relatable to the modern society. But, there is a huge difference between replicating and creating. An artist who replicates other artists work basically shows their studio skills and an artist who creates something from scratch shows their creativity, for example- The replication of Leonardo da Vinci’s The Last Supper artwork has been done multiple times, one of the famous replication of this artwork is by Andy Warhol.
This is the original artwork of The Last Supper by Leonardo da Vinci, he is one of the most famous artist and his work has been admired worldwide.
As we can see in this replication by Andy that there are not many changes, and it does not show much as creativity as the original painting. There is also a term ‘genuine fake’ where the work of the original artist is recreated by a fake artist but it is usually hard to identify since it seems to be authentic. So, although we can say that this is a replication but it is definitely not authentic.
https://www.leonardodavinci.net/the-last-supper.jsp
https://www.flavorpaper.com/wallpaper/murals/last-supper-mural