What legal issues should I be aware of if I wish to use film clips in my work?
Even images, film, audio or photographs on the Internet are protected by copyright, and cannot be used without the author’s permission.
Whilst many copyright owners ignore infringements of their copyright (or do not find out about them), action is more likely to be taken where the original work has achieved a high public profile and / or commercial success. In such a case you should try to obtain a copyright license authorizing your appropriation of the original work. If it is for a non-commercial project you will be more likely to obtain this free of charge, subject to the inclusion of an appropriate acknowledgement of the author / creator.
In addition there may be moral rights to consider, as the author of the work has the right to be both identified as such and to object to derogatory treatment of his or her work, where it has been either modified or distorted. These moral rights last for as long as copyright (i.e. for the whole life of the creator), and on death will pass for the next seventy years to the artist’s estate and then his or her successors.
You should always consider writing to the copyright owner for their permission to use the protected work, briefly explaining the appropriateness of it to your work, how the work will be shown / seen and where, and most importantly whether there will be a commercial dimension involved in the performance based work, i.e. will it generate income for you. If it's a non-commercial project, the chances are good that permission will be given without requiring payment, but with an acknowledgement being given. Conversely, if it is a commercial project then the company / owner is likely to want a one-off fee or income share for the licence.
As a general rule, only the copyright owner of film material has the right to use it, and you will therefore be running the risk of copyright infringement.