Just because something is on the Internet, doesn't mean that you can use it or copy it.
Here are some places you can go to find images for your research. All of them are free for you to use:
Image Base- Type a search in the box or browse the galleries, including City, Nature, People, and Powerpoint Templates
LIFE Photo Archive- Hosted by Google. Search historic images by decade.
Pexels- High quality stock photos
Pics4Learning- "a curated image library that is safe and free for education"
Pixabay- Free images and videos, all copyright-free through Creative Commons CC0.
The Morgue File- "Free images for creatives, by creatives"
McKinley Library - 121 East 3rd St, New York, NY, 10009 - 212-674-3180; ext. 3071 - email@example.com