Last week, a very close friend of mine called me in a panic, because she had been sued for using an image she received in email on her blog. She had not bothered to inform herself about copyright law as it applies to images, and naively assumed that if she did not see a watermark or a copyright notice, she would be able to use an image.
Not only was she named in the lawsuit, but the person from whom she leases her office was named, too! And of course, even though she is my dear friend, she went into a rant about how the law sucks, and it's stupid, and people are not informed, and all that, but in the United States, "ignorance of the law is no excuse." So before you use an image in anything you publish, whether it be an email, a blog post, an article, or something else, you need to ensure you have the right to use that image, or you, too, could wind up in court with absolutely no legal defense.
[Thumbnail image licensed for commercial use from HubSpot]