BisonTech

This plugin replace WP default admin/login/register page. 
The technique used is pretty brutal but the best currently possible, the plugin replaces the modified files automatically. 
To make the plugin run the web server must be able to write to the wp-admin directory. 
more info @ http://www.bisontech.net

LogoReplacer

This plugin replace WP default admin/login/register page.

Stencil

Stencil is the fastest way to create incredible visuals and increase your engagement on social media, blog posts, emails and presentations. Create images faster and easier than you ever imagined.
With Stencil for WordPress, you can design images as you write posts without ever leaving the page!
This 30-second video will show you what you can do with the Stencil plugin for WordPress:
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/6QkVdKyMhsE?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
Just some of the major features:
Powerful Image Editor – Designed with simplicity in mind, Stencil is a powerful but lightweight image editor that never gets in your way.
5,000,000+ Royalty-Free Stock Photos – More royalty-free “CC0” images than you’ll know what to do with! Thousands of new photos added every week!
3,100,000+ Icons & Graphics – Beautiful icons right at your fingertips, royalty-free and safe to use however you want (personal or commercial).
1,350+ Templates – Create beautiful images even faster with our premium templates, ready to be edited.
Upload & Store Logos – Upload & store every variation of your logo or different logos if you’re creating visuals for different brands. Add logos to your images instantly!
4,700+ Google Fonts or upload your own – Find the perfect font for your image by using any of Google’s thousands of web fonts! Or match your brand perfectly by uploading your own fonts directly to Stencil and use them in all your visuals.
140+ Preset Sizes – Perfect pre-loaded optimal sizes for social networks, ads, blog posts and more. Not enough? Create your own!
Instant Image Resizing – Change the size of your image without ever leaving the page or reloading.
Unlimited Uploads – Upload and use your own images in Stencil.
Favorites – Keep all your favorite photos, icons, and templates for easy future access.
Image Filters – Beautify your images with amazing filters.
Social Connections – Share to Facebook, Twitter, Instagram and Pinterest.
Collections – Create your own custom collections and keep everything in Stencil organized.
More about Stencil: 
We designed Stencil to be the fastest way to design beautiful images and graphics for your website, blog, social media channels, podcast covers, eBook covers, Facebook, Twitter, Instagram, Pinterest, or YouTube channels.
While other services (like Canva, PicMonkey, Vectr, Crello, BeFunky, Fotor, Snappa) and products (like Photoshop, Sketch, GIMP) are great for certain tasks, Stencil is the fastest way to get your images designed in a matter of minutes. If you’re looking for a great Canva alternative or PicMonkey alternative, Stencil is the one!
We support unlimited uploads, meaning you can upload your entire collection of photos and graphics straight to Stencil for use. We support all the major image types (including JPEG, PNG, GIF, SVG, WebP), and you can always download any images you uploaded back down to your computer later on.
More about the Stencil for WordPress plugin: 
While Stencil on it’s own is an amazing service, we (like you) spend a lot of time in our WordPress Admin area writing up our newest blogs and announcements.
Something we noticed while doing this is that it was a bit cumbersome switching tabs to Stencil to design our Featured Images for the blog post we were writing, download it, and then re-uploading into WordPress.
So we design this simple to use (and install) plugin so that you can use Stencil right from your WordPress Admin area.
This video will show you what that experience is like:
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/6QkVdKyMhsE?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>

The fastest and easiest way to design images as you write posts in WordPress. Millions of stock photos, premium icons & templates at your fingertips.

LogoReplacer vs Stencil