Copyright protects original works including those posted online. Works in the public domain are not protected by copyright and can be used freely. Orphan works are protected by copyright but identifying their owner is difficult. Libraries display orphan works with notices that they cannot be used without permission. Licenses like Creative Commons are types of express licenses that explain what rights authors grant for their works. Fair use is a vague concept that allows some limited use of copyrighted works without permission, though acknowledging the source does not constitute permission. When using a work, the character of the use, amount used, and effect on the work's value must be considered. Getting permission involves finding the correct copyright owner and obtaining written approval for certain uses.