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?