Havent taken that route at present but while playing curby with my boy I decided that I would make standard html form replacing the images obviously leaving the links the same.
I'd imagine Dan means <input type="submit">. That's my preferred choice for buttons as you can style them easily with images. You can't go from type="image" to type="submit" as easily.
Did you see my thread about html submit buttons in the cart? That'll sort out your cart buttons. The checkout buttons are in the library in the Checkout Buttons node, but they appear to be <input type="submit"> on my installation
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