Fair Use means you can use copyrighted material without a license only for certain purposes. These include:
Don't make money off of the copyrighted work.
In general, it's much easier to claim Fair Use when you're using the copyrighted material for noncommercial purposes. While posting images of your favorite TV shows and adding funny captions and commentary might be considered Fair Use, selling those images on T-shirts would not. Making money from ads on your blog can also limit your ability to claim Fair Use.
From Stanford University:
Measuring Fair Use: The Four Factors
Unfortunately, the only way to get a definitive answer on whether a particular use is a fair use is to have it resolved in federal court. Judges use four factors in resolving fair use disputes, which are discussed in detail below. It's important to understand that these factors are only guidelines and the courts are free to adapt them to particular situations on a case-by-case basis. In other words, a judge has a great deal of freedom when making a fair use determination and the outcome in any given case can be hard to predict.
The four factors judges consider are:
1. the purpose and character of your use
2. the nature of the copyrighted work
3. the amount and substantially of the portion taken, and
4. the effect of the use upon the potential market.
This blog is noncommercial. This blog has NEVER contained ads. No money has ever been made from this blog.