I have the following code. Just a simple image (400px) and span nested in a button (that ends up being 407px). The button has a gray background color so you can see the height difference at the bottom (on the left button). I have cleared all margins/paddings, but I can't see where the height difference is coming from.
<button>
<span>Text</span>
<img src="image.jpg">
</button>