Hi Shaik,
You can add the login image in your project directory\theme\resources folder and then add below example custom class in your styles. Apply login-image class on your top container to add background image.
.login-image {
background: left/cover no-repeat url(../../../resources/login.jpg);
}
For an example look into project directory\theme\styles\web\sass\core\base\_login.scss
For more details about adding custom styles have a look into this forum post.
Hope this helps!