Most newspaper photographers work on a freelance basis and retain ownership of their images. If you have seen an image in a newspaper which you want to reuse, you should contact the paper it was featured in and discuss the copyright terms for reuse. There may be a fee involved in reusing a photographer’s work, but you should never use it without permission.
There are also professional photography agencies such as Getty, Associated Press Images and Reuters where you can search for images. Most of these will also require permission to be granted for reuse, though they do also offer some pictures which reuse licenses available direct from their image databases. Many of these, however, cover stock photography (generic images used to illustrate broad points) rather than event-specific photo journalism.