There are many different ways and reasons for using a hidden camera. The primary reason is probably for use as a security camera. Most of these are used in businesses and can come in handy if a situation arises where there would be a need to see what was going on inside of the building.
Hidden cameras like the ones inside of an ATM machine not only capture a picture of the person performing the transaction, many times they capture pictures of other activity in the vicinity. This has been useful when trying to identify people in the area as well as their actions.
For someone like a private detective a hidden camera is an essential part of their job. It enables them to observe people and their activities without their subject seeing them and becoming suspicious. Another example of a type of employment that might use a hidden camera is an insurance fraud investigator. Again, this allows them to track the movements of an insured without them knowing they are being watched. Many times this has helped insurance companies avoid paying on a claim that is clearly a scam. This is usually accomplished because an investigator has gotten pictures of a person that has filed a claim clearly showing them performing some action that they would not be able to do if it were indeed a genuine disability claim.
More recently, hidden cameras have become a part of most schools, enabling better security as well as a piece of mind for parents and teachers. It also helps reduce the amount of graffiti that is painted on schools when hidden cameras are mounted outside as well.
Many employers have started using hidden cameras to check up on their employees and their actions when the boss is not around. Some people say that this a violation of privacy while others claim employers have every right to check up on people on his payroll. For the employers that do use a hidden camera it can be a money and time saving option. As they are able to see if the employee is spending their time wisely and performing the necessary duties or if they are simply goofing off and not completing their tasks. Having a hidden camera can also be a huge deterrent against employees, or anyone else for that matter, stealing once they know that the camera is there.
Parents are also beginning to use hidden cameras to see what is going on when they are not home. The majority of parents use them to check up on the welfare of their child when they are left in the care of a babysitter. This can prove valuable if some things are noticed right away and hopefully handled before something happens when it may very well be too late.