<em>(I'm not a lawyer, I'm not your lawyer, and this isn't legal advice.)</em>
You should ensure you have permission to use the image.
Most commonly, this will happen in one of two forms:
The image already has a free license allowing you to use it. (Generally, this will be a Creative Commons license.) Follow the terms specified and you should be all set!
If the image isn't already licensed freely online, you'll need to ask the photographer or publisher for permission to use the image. In this case, a quick email is usually enough to get the ball rolling.
In either case, you should generally have explicit permission from the person who created the picture for you to reuse and share it.
(There are some cases in which "fair use" will apply and you may not need permission from the copyright owner, but this varies on a case-by-case basis. I encourage you to do your research on that area if needed.)
A negative externality is when a good costs much greater than what the consumer pays for it. Since you did not provide the possible answers, use this explanation to find the correct answer among the ones you might have.
