In this day of digital transformation of images and sound and the haphazard distribution of audio-visual material on the net it is critical to make sure that all material used in a tape is used legitimately. This subject is extremely complicated and is frequently discussed on the net.
Some people seem to consider that because material is available on the net it is free for any use.
That is simply not the case. You may get away with using such material for your own private purposes but when you start publishing or broadcasting that material, you are letting yourself in for legal problems. Even material that you buy, such as some inexpensive sound effect CDs, typically have strict use restrictions on them. If you buy sounds or graphics to use in your production make sure that the rights you are buying are the rights you will need for your production. Most natural subjects that you record yourself are probably safe, but keep in mind that certain natural subjects may be subject to forms of copyright protection.