sorry, I was not fully clear.

It IS very much a button.

an HTML input elements type is determined by the type attribute. You posted

<input type="image" src="images/G/01/x-locale/common.....>

So it is an input element, of type image. It may feel like a button because you can click it and it does something, but that doesn't make it a button, so you can't cast it to a button element type from the MSHTML library, it simply isn't that type.

You should be able to cast it to an image element or a generic input element type, and then invoke a click on it to get the desired behavior. If you are unable to get a reference to it because it has no ID and you can't access it via the name property, then really the only solution is to loop all <input> elements in the DOM and evaluate their name property until you find the one named submit.add-to-cart, and then you would have your reference to the correct element.