Image sharing is a huge part of social media isn't it? And when was the last time you Googled to find just the right image to illustrate your point? Stop that. Stop it now! Why? Well simply put most of the images you find in a Google search may well have a copyright on them and if you don't know the source and use it anyway you could be liable for violating copyright laws.
Before you laugh me off and move on, let me tell you a story. In 1997 one of the designers at our company searched for an image of an assembly plant and then downloaded it, modified it and used it in a project on our website. In 2005 I got a certified letter from Getty claiming ownership of the image and demanding $600 or a lawsuit would ensue. Even if we removed the image, they still demanded payment. It took a lot of digging through the archives to verify what had happened and even find the image. At that point the designer had left the company and we were left holding the bag. We paid the fine and made it policy to never use images without proper attribution again.
What's all this about copyright? Isn't anything online covered by fair use? In short. NO. Here's a link to the US Government PDF on copyright, you should read it. Basically any work be it writing, images, music or other forms of work can be copyrighted at the time of creation, and fair use is a limited term. Some feel that simply linking back to the creator's website constitutes attribution and so "fair use" is indicated. That's not always true. If the original creator has not give permission through licensing or sale fair use may or may not apply.
What is fair use? Fair use is defined in section 107 of the copyright law. Specific uses like criticism, comment, news reporting, teaching, scholarship, and research may be considered fair use but it subjective, and not always easy to define. For example is blogging a form of news reporting? Let's say you are reviewing a book and you grab the cover from the author's website. The photo will not replace the original product (the book) or interfere with the author's rights, so in essence this could be fair use. Your own photo of an art installment outside used to review that art piece may also be fair use. In general it's simply better to get permission, use open source, purchase the rights or look for Creative Commons licenses in most cases.
Where can I get images? If you're looking for images check out some of these options.
Open source Open source simply means the creator allows any and all use of the image without attribution or copyright. This often is the case with software where the original code is made publicly available so that other programmers can improve or build upon it.
Free options There are several places where you can get open source or creative commons images. Way to many to list here. Follow this link to my post 12 outstanding sites for free images.
Public domain Public domain images can be marked as such by the creator, who then waives all rights to the image. They may also be particularly old images, those created by federal agencies etc and here's a link to more detail on the public domain mark and it's use.
Creative Commons Another way to find images to use is to search for Creative Commons licensed images. There are several different licenses available for creators to choose from and you should familiarize yourself with each. Basically they range from images OK to use with attribution to the source for commercial and/or non commercial use to all rights granted images which you can use any way you like.
Stock Stock images come in many forms and many price ranges. Some may be as little as a few cents each and others hundreds or thousands of dollars. It varies by the quality of the image and the perceived value. Clearly a newsworthy photo may have a higher price tag than a photo of a more traditional stock image. Some have limited time allotments and others allow you to purchase image rights indefinitely and use them in any way you choose. Check the rights on the image before you buy them to see what uses are allowed.