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!

Kerry Webster

Features of the Branded Login Screen plugin:
<ul>
<li>FULL SCREEN BACKGROUND IMAGE</li>
<li>USE YOUR OWN HEADER IMAGE IN PLACE OF THE WORDPRESS LOGO</li>
<li>POSITION LOGIN FORM: LEFT, CENTER OR RIGHT / TOP, MIDDLE</li>
<li>LOGIN FORM IS RESPONSIVE FOR SMALLER SCREENS</li>
<li>SCROLLING OF FORM IF OUTSIDE OF VIEWPORT</li>
<li>BACKGROUND IMAGE SIZES WITH WINDOW RESIZE</li>
<li>REPEATING BACKGROUND IMAGES SUPPORTED</li>
<li>REMOVES ALL WORDPRESS BRANDING</li>
<li>STILL UPGRADE PROOF</li>
</ul>

Branded Login Screen

Update the WordPress Login Screen to use a hi-res, full screen, resizing background image. Now completely responsive.

Login Logo vs Branded Login Screen