I changed the image and had problems with the size and alignment. Now I have set the following CSS styles and so the image is set as background for this column. This way it looks great even with different screen sizes.
.lpx-login-image-area img {
display: none;
}
.lpx-login-image-area {
background-image: url("/Themes/LeptonX/Global/assets/img/login-bg.jpg");
background-position: right;
background-repeat: no-repeat;
background-size: cover;
}
