The answer is that YOU don't, you see someone who knows how to do that. We call that person a copyright attorney or entertainment attorney. The attorney will advise you on where and how to find out or do it for a fee for you. Older ones may or may not be okay to use. Google images will often give you a good clue. Amount of dissemination is irrelevant to copyright status, that is more relevant to trademark status - another concern you did not mention and another reason to see that attorney. You won't necessarily need the attorney for each photo once you get the hang of how to check and clear them, but starting out you really don't want to make mistakes that could get you a CDL from Getty Images or other aggressive stock photo seller. That could turn a $3 photo into a $3500 nightmare for you.
I am not your lawyer and you are not my client. Free advice here is without recourse and any reliance thereupon is at your sole risk. This is done without compensation as a free public service. I am licensed in IL, MO, TX and I am a Reg. Pat. Atty. so advice in any other jurisdiction is strictly general advice and should be confirmed with an attorney licensed in that jurisdiction.
You have another problem besides determining which photographs are protected by copyright (and counselor Burdick has given you good advice on how to go about doing that) and that is your intent to use photographs of famous people. Most famous people have rights to protect how their images are used. States have right of publicity laws which protect a person's image from being used without their permission, especially when used for commercial gain.. Even if the person is dead, their family or estate may still retain these rights. Another reason to see an attorney experienced in your state's laws.
You should consider who else owns the rights to the photograph and have a copyright lawyer assist you in securing licensing agreements for the photographs you wish to use. Generally, the photographer or a stock photo company owns the image, but since you are considering using images of famous people, you must consider that individuals have the right to prevent the use of their likeness or name from being exploited for commercial gain. So you will need to have an attorney address both of these issues. The kind of use that you make of the person's image may or may not be a misappropriation. This is definitely worth considering a copyright lawyer. If you are developing a game, you will also want to ask an intellectual property lawyer about how to protect your game and whether the features of your game could potentially put you at risk of infringing on someone else's copyrights, patents or trademarks. The companies that deal in photographs and other intellectual property are often very serious about protecting their intellectual property and its value - because that is their business.