The purpose and character of your use
This is the first copyright fair use factor. This means that you can take someone’s work and change it. But you have to transform the work. You need to add a new meaning or expression to the work. Also, you need to add new information, new aesthetics, new understandings from the original work.
The Nature of the Copyrighted Work
This is the second copyright fair use factor. This gives you some more leeway to copy from fact based works like novels, plays, and biographies. Also note that you will have a stronger case if you copied from a published work than an unpublished work.
The Amount and Substantiality of the Portion Taken.
This is the third copyright fair use factor. Obviously, the less you copy. Most likely you will be excused as fair use. But, even if you take a very small amount of work. If what you took was the “heart.” Then you will most likely run into some issues.
The Effect of the Use Upon the Potential Market
This is the fourth and final copyright fair use factor. If you deprive the copyright owner of their income, this will most likely trigger a lawsuit. You are basically stealing their money!