Hi,
In general, the answer is yes. You can take an Auctiva stock template and create a Custom template with your own images.
I looked at "Going to the Dogs". That dog image is a composite of two image pieces placed as part of the upper template border.
Here's the left portion of the image:
Here's the right portion of the image:
As you can see, the collar is part of the image and probably makes the replacement more difficult.
Danno