João Luís

WordPress allows you to define a site logo (through Jetpack) and a site icon, why would you need to upload another image to use in your login page?
This plugin allows you to forget the login page. Just activate it and all the magic is done for you. No extra steps required.
The plugins uses the site logo if it exists, otherwise it will use the site icon. If none of them exist, the plugin will not touch your login page.

JL Login Logo

Uses your site logo (defined through Jetpack) or your site icon as the logo on the login form.

bozdoz

<a href="https://wordpress.org/plugins/jetpack/" rel="ugc">Jetpack</a> makes it easy to add contact forms to your WordPress site, but you may want a simple way to add a <a href="https://www.google.com/recaptcha/" rel="nofollow ugc">Google reCAPTCHA</a> to prevent spam. This plugin will manipulate the Jetpack <code>[contact-form]</code> shortcode to prepend the Google script, add a button, and parse the response.
This plugin allows both reCAPTCHA v2 and invisible reCAPTCHA (see screenshots and choose whatever works for you!).
Shoot me a question about it on Twitter: <a href="https://www.twitter.com/bozdoz/" rel="nofollow ugc">@bozdoz</a>.
This plugin is open source on <a href="https://github.com/bozdoz/wp-plugin-recaptcha-jetpack" rel="nofollow ugc">GitHub</a>!

reCAPTCHA Jetpack

A simple plugin that adds a Google reCAPTCHA to the Jetpack contact form. Requires the Jetpack plugin.

JL Login Logo vs reCAPTCHA Jetpack