I thought this was an interesting article about credit card skimmers. It goes in depth and shows picture examples of credit card skimming techniques and how to best protect yourself.
For starters, it’s a good idea to give a gentle tug to any part of the ATM that sticks out. The reason for this is because it could be a non-factory (malicious) piece glued on with skimming technology for the card or a hidden camera to record your pin. The most simple protection is to use your hand to cover the keypad when entering your pin. Another suggestion is to use ATMs at banks, rather than one on the corner of a street or in a convenience store that might not know what to look for.
An important thing to take away from this is that the move towards chip cards in the United States doesn’t make card skimming issues go away. The magnetic strip is still required to use an ATM as a way to ensure the card is inserted properly.