How to find information about copyright law
We are surrounded by copyright law. Every book, CD, DVD and magazine will have a short, direct paragraph telling you that any copying, reproduction, public viewing, editing or other use of the content is forbidden unless you have the publisher's specific permission. There are a few areas of exception. Schools can use certain material for teaching purposes and it is generally accepted by publishers that ripping a CD into MP3 files and storing them on a device for private listening is acceptable. This started in the days of cassette players when people were recording discs onto tape to listen in a car. Although not 'allowed' in the strict letter of the law, it is tolerated as reasonable activity, a bit like smoking pot in Amsterdam.
So where does this leave us in terms of sourcing and using material on show reels etc. Well the simple truth is you can't do it. By copying a TV programme and then editing out your bit you are directly contravening the copyright. Obviously if the nice people at the BBC send you a copy then they are implicitly giving you permission to use it. In the case of show reels that are being privately distributed, I suspect there aren't many at the Beeb or Sky that really worry too much about it. They could but they don't. The same applies to pictures and YouTube. Most of the material up there is owned by someone else. Copyright of images always stays with the originating photographer except in the case of pictures featuring the Queen. She owns the copyright to every image of herself. Luckily she's quite relaxed about it and doesn't seem to make a fuss. If someone snaps a shot of you while they are standing in a public place, they own that picture forever and there is not much you can do about it. If you are in a private place and they trespass to get the picture then it's a different matter but you will need the courts to side with you. Catherine Middleton will tell you how unfair that is if you get a chance to ask her.
To be completely safe you would need to originate all your pictures and video yourself, an unlikely situation. Even if you filmed yourself knocking out a quick soliloquy, do you have the permission to perform the words? They will be subject to copyright for 70 years after the originator's death. Older material does clear copyright restriction eventually and then it is only a courtesy to ask the publisher for permission to perform it.
All this is enshrined in quite a bit of complex and wordy legislation. For more detail have a look at
The simple message is be aware that you may be are using material illegally and if someone decided to get stroppy you could wind up in court. Within that context, be sensible and consider the issue before copying, editing, publishing or otherwise mucking about with anyone else's work. How would you feel if someone did it to you?