For html images, you don't want to put BBCode (or whatever the square bracket stuff is called) into it, since you are just doing html.
As such, just get rid of the unnecessary tags.
<img src="url">
Url is just the link to the image.
A good idea is to also add 'alt', which is alternative text, that way if the image fails to load (or if someone is using a screen reader) they can still know that there is an image there and what the image is.
<img src="url" alt="Text description of the image.">