There are many defintions of art and what separates art from a more common form, but if you accept the definition of art as
"... the product or process of deliberately arranging symbolic elements in a way that influences and affects one or more of the senses, emotions, and intellect..."
then films that fit this description must certainly be considered art. A certain mastery or skill level is to be expected, and a true piece of art is intended to stimulate "thoughts and emotions": They must be aesthetically pleasing.
Art is not just restricted to paintings and sculptures, but can include forms such as film, music, literature and photography. Obviously, art is seen from the eye of the beholder: A young child's attempt at finger painting may not be seen as artistic to most people; however, the parents of that child are likely to be emotionally attracted to such an effort, and they may consider it a true work of art. The same can be said of films. Movies such as Citizen Kane and Casablanca are rich in symbolism and have garnered a strong reaction from viewers through the ages; most critics consider them among the best films ever made, and they fit the description of film art. Even certain aspects of filmaking, such as the acting and editing, can be considered artistic. And, there is the belief that any film made is a work of art, since it encompasses a certain skill level and, presumably, intitiates an emotional response from at least some of its audience.