Creative Commons develops copyright licenses designed to enhance the sharing and creative reuse of digital content. Copyright owners may choose to license their materials under one of several licenses with various requirements or limits on reuse, such as attribution required or no commercial use.
Learn more about using Creative Commons licensing - for your own work or for reusing others' work - at the links below.
Creating your poster may be entirely original work on your part, but if you use text, images, or designs from another source, you need to be aware of copyright. If an item is under copyright, there are limits on whether, how, and how much of the item it is fair for you to reuse.
Credit: Copyright symbol. From "Copyright" article in Wikipedia.
If you use another person's work, you need to acknowledge it, usually by citing it.
The links below will help you locate information regarding appropriate citation styles.