DISCLAIMER: using icons or gifs that are not owned by you are solely and completely on your responsibility. You should check the terms of use and copyright of each icon or gif that you decide to use on your websites.
NOTE: You can also use animated gif icons, you can try giphy:
Here's a guide for using icons8
Start by visiting https://icons8.com/
Search for an icon and click it
Click "Download"
Click "Link (CDN)"
Copy the image URL in the src part of the snippet
<img src="https://img.icons8.com/ios-filled/50/welfare.png"/>Paste the copied link into the Image input in ProveSource.
Learn more about customizing the icon with icons8 URL formatting here: http://img.icons8.com/