Niaj Morshed

Just Install the plugin, then you can see the login form has changed, 
after this go to the Settings->custom-login & put your logo & background image link which you want. 
Enjoy.

wp Custom Login

This plugin can changes the logo & background image of the login form.

Johan van der Wijk

Customize Admin is a powerful WordPress plugin that puts you in control of your website’s login page and dashboard layout. With its intuitive features, you can effortlessly tailor the look and feel of your WordPress login page and dashboard, creating a seamless and branded experience for your users.
Key Features:
Personalized Login Screen: Easily upload your custom image or logo to the login screen and define the link associated with the logo. Take your brand identity to the forefront and leave a lasting impression on your visitors from the very first interaction.
Streamlined HTML: Trim down and fine-tune your website’s HTML source code by selectively removing meta tags from the head section. Enjoy better control over your site’s code and optimize it for improved performance and SEO.
Dashboard Widget Management: Take charge of your dashboard widgets! Customize Admin enables you to disable selected widgets, allowing you to declutter and streamline your WordPress dashboard effortlessly.
Want to see the magic of Customize Admin in action? Check out the <a href="http://www.vanderwijk.com/wordpress/wordpress-customize-admin-plugin/" rel="nofollow ugc">plugin homepage</a> for more information and an enlightening screencast video that showcases the plugin’s capabilities.

Customize Admin

With this plugin you can use customize the appearance of the WordPress login page, dashboard and head section tags.

wp Custom Login vs Customize Admin