I've seen some people struggling to add inline images either in posts or comments.
Here's a quick example how I do with Imgur. Assuming you have already created an Imgur account
Select add images button and select the desired image. After uploading it, Imgur will display this page
Choose the image you want to add on IH and copy the Markdown link value
Paste the markdown link adding the exclamation the point before the [ character. It can be done either on post or comment.