After you're logged in, when you reply to a thread, there are a set of small buttons above where you enter your text - B, I, U, etc. One of the buttons is a camera icon. You can hover your mouse over the icons for tooltips. This one says - Image Upload.
Click it and it opens your account's Image Upload interface.
Then, when you click on your uploaded image, it gives you the image's embed code. Copy/paste that code into your comment.
*Please remember to Like an answer if it solves your question or gives you a good idea.