/* Hide the image by default (desktop first approach) */
#mobile-123 .mobile-only-image {
  display: none;
}

/* Show the image only when the screen width is 768px or less */
@media screen and (max-width: 600px) {
#mobile-123 .mobile-only-image {
    display: block; /* or inline-block, depending on your layout needs */
	width: 100%;
    height: 300px;
	border: 1px solid #000000;
    background-color: #000;
    overflow: hidden;
	position: relative;
  }
}