If you are looking for free royalty free stock images to plug into your articles, an excellent site that I have used for presentations and the like is the stock.xchnge. The key is to be careful in reading what the photographers have labeled as acceptable use for their photographs. For example, the photo in the image used in this post has a license as follows:

You may use the Image

• In digital format on websites, multimedia presentations, broadcast film and video, cell phones.
• In printed promotional materials, magazines, newspapers, books, brochures, flyers, CD/DVD covers, etc.
• Along with your corporate identity on business cards, letterhead, etc.
• To decorate your home, your office or any public place.