How do I find photos of a country for my research paper?

A good source is the CIA's World Factbook website (linked below), from the U.S. Central Intelligence Agency (yes, the CIA!). 

Go to that page and search for a country. On the main page for the country, look near the flag and the map for a link to photos. These tend to be better quality than just using Google Images. Please give the photographers credit, however - if it's not yours, it's someone else's. 

You can also click the drop-down menu on their homepage for current information about each country and political entity in the world: politics, geography, economy, people, military, communications, energy and other issues, as well as flag, national anthem and, often, selected captioned scenic photos. The photographers usually owns the copyright to these images, so treat them accordingly. 

Make sure to cite your sources, no matter where you get your information!