If enough people believe something is art, then it's art. This can change. And it can be manipulated.
So if you give colors, a linen canvas and a paintbrush to a 2-year-old and ask him to paint "something colorful" then it's usually just a kiddie-picture. If you secretly put that picture on a wall in a modern-arts museum and put a sign next to it that says "Whirling colors; piece 3 of series 7", people will stop in front of it and believe it is some piece of modern, abstract creative expressionism.
To be honest, I think all art should be legit. As long as a person is not trying to pass someone else's work off as their own. I have literally seen crumpled up trash in an art exhibit. Honestly, if you would see some of the things people consider art these days, there is no way you could exclude something from that group. Oh, and don't get me started on performance art....But what do I know......I like science.
Good question. I think the story or idea behind something for example, I believe that anyone can draw or paint if they really put effort into it, but it takes a good artist to convey a message or to try a new technique etc. But it is still very much interpretation.
Art like beauty is in the eye of the beholder. There is no objective test to determine how artistic something is.