If you are not a paying member, you need to host the pictures at a third party site. I use Imgur. I stole these instructions from
@Thomas Linton:
USING IMGUR TO POST PICTURES ON A FORUM
Create an account (free) at Imgur.com. Create an Imgur name, like a forum name here.
Click on "Browse" at Imgur (which automatically appears when you open IMGUR,) to find a picture you have saved (probably in the "picture" file) on your computer.
"Open" the picture you want to copy or "drag" that picture to the IMGUR screen (you will be prompted as to where to put it by IMGUR.). This saves the picture to Imgur.
Put cursor on your IMGUR name at upper right to drop down a menu of actions.
Click on "[your Imgur name] images" on the menu that drops. Images that you have saved to IMGUR will appear in a grip to the right.
Click on the image in the page of images that you wish to share here.
On the right side of the screen, a list of options appears. Click on blue "Copy" tab on "BBCode" from the list.
Go to forum page where you want picture to show up and "paste" link you just copied from Imgur on that page.