Image appears a white border underneath

Question

Guys, I made one button and within this button, I put an img. On the site, the image has a white border underneath. I’ve already removed the edge of the button by CSS and still it continues. Which property is it that is giving the edge? I want to remove it.

Obs: she just shows up underneath.

HTML code:

<article id="almoco">
<header class="categoria">Almoço</header>
<figure>
<button>

CSS of the image:

  img {
        max-width: 100%;
    }

CSS of the button:

  button {
        background-color: #FFFFFF;
        border-style: none;
    }