Takes some HTML and CSS.
So once you added your image, switch to the text editor. And wrap your Image with this HTML and include the span tag for your label:
<a href="url-link-goes-here" class="img-button">
<!-- Your <img /> goes here -->
<span class="img-button-label">Image Button label</span>
</a>
Then add this CSS:
.img-button {
display: block;
position: relative;
}
.img-button-label {
display: block;
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
padding: 40px;
display: flex;
align-items: center;
/* Font styling here */
font-size: 24px;
font-weight: 500;
color: #f00;
}