Mark Jaquith

This plugin allows you to customize the logo on the WordPress login screen. There is zero configuration. You just drop the logo file into your WordPress content directory, named <code>login-logo.png</code> and this plugin takes over.
Note that you should use a transparent background on the PNG image, crop it tightly (no padding pixels) and use a width of exactly 312 pixels for best results. Wider images will be downscaled in modern browsers, but it isn’t recommended to rely on that.
This plugin also works in the <code>mu-plugins</code> directory.

Login Logo

Customize the logo on the WP login screen by simply dropping a file named login-logo.png into your WP content directory. CSS is automatic!

sureshdsk

Use wp-login customizer to change wordpress logo,background image and Powered by wordpress.org link on your wordpress login page. 
More information: <a href="http://www.cloudwark.in/wp-login-customizer-wordpress-plugin" rel="nofollow ugc">wp-login customizer</a>
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wp-login customizer

Customize wordpress logo,background image and Powered by wordpress.org link on wordpress login page.

Login Logo vs wp-login customizer