Here’s an article worth reading.
A company that writes blog posts for commercial clients was sued $8,000 for posting a copyrighted photo on a blog site. Through lawyer negotiations that amount was reduced to $3,000. Apparently this is becoming more common as there are services for hire that run programs 24×7 to search web pages for copies of your work.
The key is to be aware and stick to the rules!
Here’s a link to WikiHow’s page on avoiding copyright infringement.