Disclaimer: Intellectual property (a.k.a- I.P.) is a complex and evolving area (that even some lawyers don't understand very well). This post is written from my perspective as someone who used to work in the I.P., art rights industry. I am not a lawyer- so it should not be construed as legal advice. For specific questions you should always consult an attorney who is qualified in this area of law.
For artists there are generally two sides to the intellectual property coin- creation and use. In this post we'll focus on creation, in part 2 we'll talk about use.
Fast Track, copyright Meg Bandarra, All Rights Reserved
Lets start with the basics- what is intellectual property? When you create something (e.g. a drawing, a painting, a design, a song, a performance piece, a story, or a photograph) you have inherent rights to these artistic pieces, which means you control what happens to the them. Who can use your work in publications or shows, whether or not derivative pieces can be made, whether or not reproductions can be produced, are the types of things your intellectual property rights give you control over.
A common misconception about intellectual property is that it covers ideas, sadly that's not the case. In order to have rights over something you have to create it. For example: if you have an idea for a sculpture and verbally discuss that idea with a friend (who's also a sculpture) and later you find out your "friend" has create a sculpture based on your idea, they might be a crappy friend... but they have not infringed on your intellectual property rights. If however, you made a sketch of your idea, showed the sketch to your crappy friend, and later found they'd made a sculpture based on that sketched idea- that would likely be infringement (even if you never made the actual sculpture yourself). You have I.P rights over the sketch and your "friend" has likely made what's known as a derivative work.
That's not to say an item has to physically exist in the real world for you to have rights. A photographer who takes a digital photo that's only ever displayed on social media still has intellectual property rights for that photo. Things on social media are not a free-for-all. Unless specifically expressed otherwise, only the person who took the photo is allowed to use or display that photo.
As soon as you create a piece of art you automatically have rights for it. You don't have to register it in order to have copyright protection (although it does make it easier to enforce your rights). Mailing yourself an envelope to prove a "creation date" is a myth, so save yourself the postage.
Every human that creates a piece of art has intellectual property rights to it. It doesn't matter what their age is (so yes, a toddler has I.P rights to their drawings). Interestingly, whether or not you have to be human to have I.P. rights was challenged in court when a monkey took a selfie on a photographer's camera. But when the case went to court, the "human" requirement was upheld.
When you sell a piece of art, as the creator you retain your I.P. rights over the image. The buyer can't make greeting cards, new prints, or anything else using the image, without having the artist's permission. The artwork also can't be published without your permission.
This holds true even for commissioned pieces- as the creator of the artwork you hold the I.P. rights. Although artist's retain the rights to commissioned paintings, it's always a good idea to make this known in your commission contract, just so it's clear. A word of warning though, if you're using someone else's photo as the inspiration for the commission (e.g. the client provides a photo of their dog for you to paint)- the rights to the new artwork get murky because you're likely making a derivative piece, or possibly even work-for-hire art. At the very least, you should make sure you have permission to use the photo... but that get's into "use" which we'll talk about in Part 2.
Work-for-hire v.s. Commission: In a work-for-hire scenario the employer owns the copyright, not the artist. If you're an illustrator employed at a large animation company, the company owns the artwork you produce as part of your job. This is a very clear work-for-hire scenario. Work created by an independent contractor is also owned by the employer, not the artist. Deciding whether artwork is a commissioned or a work-for-hire piece is sometimes not so clear. It can come down to slight differences in the amount of supervision or direction that the artist was given, the source materials, and even the type of work that was produced. So the best course of action in a commission or work-for-hire work scenario is to have a contract that clearly outlines who owns the rights to the work.
Remember, copyright and intellectual property are complex issues that can also vary by country. Reading something on the internet is not the same as talking to an attorney. If you're looking for legal advice, seek out a professional who specializes in this area of the law. :)