Quite often the most interesting shots are taken not by professional photographers, but by amateurs
Many countries have photo libraries that accept high-quality travel photographs. Photos are provided on a temporary basis to agencies, which in turn rent them to clients (these can be both publishers and advertising agencies). Most photo libraries offer to share profits from photos equally. They usually determine the required number of accepted photos, the minimum storage period for your images, and require at least one year's notice before withdrawing files. They also give preference to professional photographers who regularly submit images.
It is best to contact the photo libraries before your trip – this will allow you to find out in advance what they need. Many libraries provide useful technical advice. Never send poor shots just for quantity, as this will spoil the overall impression.
You can also contact the editorial offices of newspapers and magazines in your city. After all, the services of photo archives are not cheap, and images from abroad are needed by every self-respecting editorial board.
Even if you are not particularly successful with a camera, you can benefit from being in the right place at the right time. It doesn't matter whether you are in a foreign country or have gone on a vacation in the Moscow suburbs. Earl Young held an interesting opinion on this, claiming that not taking a camera on a trip around the country is simply stupid. What if an incident of international significance happens right in front of you on the street, and you don't have a camera with you?
If you actually take a picture of a terrorist attempt or any other event, without wasting a minute, contact news agencies. The most famous of them have offices or representatives in most world capitals. If newspapers around the world start buying your shot, you won't have to work anymore.
The easiest way to become a photographer is to take pictures of people on the streets, beaches, near monuments, in cafes, etc. It is said that even on nudist beaches there are many who want to be photographed, but it is better to agree with clients before you 'click' them, otherwise they will 'click' you.
Here is another way to earn: a certain Michael Jenkins came up with the idea of taking photographs of tourists during their first trip to Corfu. Most of those who showed only moderate interest at first liked the photos so much that they gladly paid 4 euros for three shots. Such a combination of pleasant and useful activity.