Check the account history of the source. Two red flags are: the number of posts and how long the account has been active. If it claims to be a well know source(like CNN or CBS) and only has a few posts in its history that is a clue. If it's a well know source and the account has only been active a short time that is another red flag.
Images of an event are often reused to deceive people. You can check if an image has been used before on a reverse image search service like TinEye.
Which of the following accounts is fake? How can you tell?
Nearly all of us have been taken in by a video that was later found to have been doctored or faked. It is fairly easy to edit a video so that it looks like you made the basket or the hawk picked up the snake. Here are some of the most famous faked videos that fooled millions:
These Viral Videos Were Fake?!
Some tips to help you tell if a video is fake: