Copyright and Fair Use

What I am doing is educational, therefore it is fair use.

Just because your use is for a non-profit educational purpose does not automatically give you permission to copy and distribute other people's work.  'Educational purpose' is only one of the four factors relating to a fair use determination. To decide whether a use is a fair use, the effect on the market, the amount used, and the nature of the work must also be taken into consideration.

I am not making any money from the use, therefore it is fair use.

Effect on the market is only one of the four factors relating to a fair use determination.  Whether or not you are making money does not matter so much as whether you are replacing the market for the item, for example if people can view your item instead of having to purchase it.  To decide whether it’s a fair use, the effect on the market must be taken into consideration along with the other three factors: amount used, the purpose of the use, and the nature of the work.

If I am making money from the use, it cannot be a fair use. 

Even commercial uses can be fair use. It’s all about the balance and weighing the four factors to come to a conclusion.  If other factors are in favor of a fair use, it may balance the fact that you intend to make money from the use.

So long as I am not using something that is entertaining, it can be fair use. 

Copyright is concerned with originality, not quality.  Whether it’s high artistry or low budget B movies, anything that is an original and tangible creative expression receives copyright protection according to U.S. law.

As long as I provide proper attribution for a use, I do not need to seek permission.

Attribution is a matter of ethics and responsibility, but it has no bearing on a fair use assessment.  To determine whether you have a fair use, you will need to go through the four factors assessment according to your intended use.   

So long as I only use a screenshot or a still from a film it will always be fair use. 

Even the smallest bit of a work including screenshots or stills can have copyright. There is still copyright in small portions of a work. You must make your own fair use assessment of the little bit you want to use. It may be a fair use to use a screenshot or still - but you still need to look at each use in light of all four factors and the overarching purpose of fair use.

I only copied 10% so it must be fair use.

There are no "bright line" rules for fair use; guidelines are not the law. A small amount could be the heart of the work and not fair use. There are no numeric rules, and that's a good thing--you'll want always to have the right to exercise judgment on what amount/which content you might need to use within your work.

If it is fair use in the classroom, then it must be fair use to use it online.

There are different facts to consider when copying materials for online use, particularly when considering use of media or other visual works online. A fair use analysis must be conducted for online use same as for classroom use.