On your login page you will have probably seen the WordPress banner, just above the login fields, a million times. You may not have paid that much attention to it but I will go out on a limb and wager that you have thought, at least once, whether it would be possible to replace it.
Replacing that banner with one of your own is actually incredibly easy.
1. Get your banner and shrink it to 310 x 70 (I guess you can use any size but this is the size of the WordPress banner).
2. Open up your FTP client and go to wp-admin → images → and find logo-login.gif.
3. Replace that file with your own image, don’t forget to call your image logo-login.gif.
4. That’s it. You should now see your chosen banner on the login page now.