Blogs have the toolbar above the typing area (like how forum posts and replies do) and you can hit the image icon, where all you have to do is get the image's direct URL. You can also use the <img> tag (<img src="*insert image URL here*">) when the toolbar isn't there, such as is the case for profiles.
In order to get an image's URL, you'll usually need to post the image on an image hosting site (ex: ImgBB or PostImages). Once you do, the site will provide you the direct URL for it