* The Impressum is where you list your contact information. This page is mandatory for all commercial websites operated by a German person or organization, even if the website is hosted in another country or has a .com domain1. A personal, non-commercial website does not need an Impressum1. In other words, if you live in Germany and use your website to make money or promote a business, you need an Impressum.
If you use images with a Creative Commons licence, make sure you properly attribute the author. In Germany, using the wrong attribution format can be a costly mistake.
If your website generates income, it's a business. If it's not part of a registered business, you will need to register it with the Gewerbeamt and the Finanzamt.
The Telemediengestz says that ads on a website must be clearly labelled. You can't disguise an ad as genuine content. Otherwise, it's surreptitious advertising (Schleichwerbung), and you can get an Abmahnung for "unfair competition".