Visit morguefile for a wide selection of images. Although a few photographers on the site request that you contact them before using their photographs, most do not. Credit any photo you use even if nothing on the site says it is required.
Check sxc.hu, where some professional photographers donate a few images for free use. Provide credit to the photographer for any image you use, and credit the site in the credit field of your article. Read the terms of use under the photo. Some require written permission. Do not use a photo with the expert watermark. These photos must be purchased.
Visit government sites for public domain pictures. Any photograph taken by a government employee during the course of their work is public domain and can be used without permission or compensation. Credit the photographer and the office.
Look for celebrity photos or news photos in the press section on their web pages. The free photos will be clearly labeled, and the site will explain if there are any limits to how they can be used.
Browse the images at everystockphoto. A search on this site will bring up thousands of photographs and images. Most are free to use as long as you credit the original photographer. Some require a link back to everystockphoto. Check the license requirements for each photo you use.