ok...guess i will have to be more detailed since you havent figured it out yet...once you have the URL (right-click an image and go to properties,copy that link)...there are 2 ways to go about it,you can choose to do it manually if prefer to just use quick reply and not have to worry about going to the post reply screen,or just have the forum wrap the tags for you so you dont have to...but that option is only accesible from the "post reply" screen...either way is real simple
manually: easy formula
....put the URL in between those tags,pretty straight forward
auto: in the post reply screen,there is a button that is called "insert image" it looks kinda like a mountain top,hold your cursor over it to find it if you dont recognize it,the tool tip will pop up....click it and it will bring up a screen for you to enter your URL...simply paste it in the box and you are done,it will do the "IMG" tags for you