Hi @
,
You've got a couple of options. My response on generating content for newsletters here might help you if you want to have more flexibility.
But to solve the examples you gave, all you need to do is plug in a field merge into the URL. Here is a post that covers placing a field merge in a URL.
Example:
<img src="http://www.yoursite/<span class='eloquaemail'>YourFieldMergeNameHere</span>.jpg" />
I have not tested the above. You may need to play around with it a bit. Please let me know if you need any help implementing this.