Here's how you do it:
First, you must download one (or both) of the images to your hard drive. Then, you would need to upload them to your webhost.
For the animated gif, here is the code you would add:
Code:
<a href="http://stamp-shack.com"><img src="http://yourwebsite.com/AnimatedShack.gif"></a>
Here is the code for the still gif
Code:
<a href="http://stamp-shack.com"><img src="http://yourwebsite.com/StampShack.gif"></a>
Replace the 'yourwebsite.com' portion with the exact location/directory in which your image is uploaded.