User blog comment:Trellar/Screenshots: Tips & Tricks/@comment-954127-20120329224333/@comment-166269-20120330210022

Strictly speaking, there is no legal issue with taking screencaps from other websites (beyond potential fair-use violations, which can be an issue regardless of the screencap's source). Just because you take a screencap doesn't mean you suddenly have a copyright on it, even if you manipulate the image somehow - crop it, rotate it, change colors, add a watermark claiming the image is copyright to you, etc. If someone complains that a screencap on your wiki is from their website and you need to remove it, therefore, you can ignore them because they don't have a legal leg to stand on; copyright law is very clear about this.