Add a custom logo to your wp-admin and login page.
Works on multisite installations.
However, the image you use must be within 80x80 pixels or it will be cropped to that size in WP 3.8.
To clarify: note that adding the image to the admin area places it to the right of the left side menu, above admin area content. It does not replace the WordPress logo at top left (within the top bar).
You must log in to submit a review. You can also log in or register using the form near the top of this page.