Copyright investments are a big business shelling out over $6 billion a year in royalty income. Every time a song is bought or played for a commercial pursuit a royalty is paid to the owner. These investments can generate some hefty returns that consistently bring in 10-15% returns on investments. Along with a potential capital gain later on.
One of the most famous is the purchase of older Beatles songs by Michael Jackson in 1985 for almost $48 million. He later merged these songs with others and eventually sold them for almost $1 billion.
There's a problem for most of us though. Unless you've got over a million in investable assets the govt doesn't want you to have anything to do with this industry. They don't consider you "sophisticated" enough to do it. Maybe they're right because it can get complicated. Here's a few points...
Taxes: copyrighted material can be amortized over 10 years so you lost likely won't have to pay any tax on your income during that time. However, if you ever sell it than you have to pay ordinary income tax on the amount you amortized and then capital gains on the amount above that.
Legal: anything copyrighted after 1/1/1978 has a copyright for 70 years after the last writer's death and then reverts to the public domain meaning you no longer get royalties. All of this needs to be researches and known prior to purchase so that you can figure your investment return.