1st. Go to any image hosting and upload a file (i will be using imgBB for this example)
2nd get image as shown in screenshots:
3rd. Use ! [] (imageurl) (Without space between !,[] and ())
Result:
(And yes for this guide i borrowed image from Wikipedia, for some reason)
Keep in mind that many image hosting sites are banned in some countries or on some networks. I'd strongly recommend just using Gravatar as it's what the site already uses for profile pictures
wikipetan my beloved