Image Optimization for Web Developement

I am building a section in my website where I will be including a mail image. The image will be small and I am using this because I wasn't able to find out how to include fontawesome.com into my website. So here's my question. Would there be any difference in the performance of the website whether I use icons from fontawesome or images from the web? The next part of the question, is if the answer is it's better to use icons from fontawesome.com, how can I use it perhaps cdn? And if the answer is image or it doesn't matter, would be okay to use the online url of the image or have it locally. For me, as long as the performance difference isn't too big it's fine.

I don't have any codes to include