This was very useful and informative. Thanks.

I'd just like to point out the importance of providing suitable alternative texts for image headers. Alt texts are especially important for accessibility purposes for people with disabilities. In markdown, the alt text goes into square brackets, such as:

![alt text](imageurl.jpg)

In HTML, it is defined using the alt attribute. For example:

<img src="smiley.gif" alt="Smiley face" />