See the video for live demo. I used the Genesis Sample Theme. But you can add this effect in your child theme. Follow the steps at below:
Uploading Mini Logo via Theme Customiser
Before editing the files you will keep a backup of your file theme. Open the lib/customize.php file and go to end of the file. Add the following PHP script above the last closing bracket (}):
If you need any help, feel free contact me via contact page.