Copyright violations are an area of concern for the podcaster. You cannot use the creative work of another person without their permission. You cannot use commercial music from artists such as the Beatles, Celine Dion, or Bruce Springsteen in your podcast or videocast. Music that you hear on your FM radio is almost always off limits for the average podcaster. Therefore it is best to use your own creative work in your podcast or blog. Or, use music or other creative works that are licensed under a Creative Commons license. The basic Creative Commons licenses allow you to use the creative works as long as you give attribution to the creator.
From that point the Creative Commons license becomes more restrictive only allowing use for non-commercial purposes, non-derivative use (you must use the original) and several other restrictions or a combination of restrictions. What this means without getting too technical is that you have a lot of opportunity to use music and other creative works in your podcast. If you want to learn more about the Creative Commons licensing you can visit the Creative Commons website.
There are several exceptions to the copyright law including use for educational purposes, parody and non-commercial use. The exceptions are very specific and you should consult an attorney if you want to use copyrighted material that might fall under one of these exceptions.