AB's server doesn't accept images (except, of course, for avatars).
You need to upload your picture to an image-hosting website and then post a link here. Tinypic is the preferred option of most people because there's no registration process.
You don't need to use PhotoPlus (or any other software on your computer). You simply need to know the name of the file and its location (e.g. the 'My Pictures' folder).
Go here:
http://tinypic.com/
Click 'Browse'.
Navigate to the location of the image file and double-click on it.
Click 'Upload now'
Copy the security code into the box and click 'Upload now' again.
When the picture appears, left-click in the 'Direct Link for layouts' field (to highlight the text).
Then right-click and select 'Copy'
Come to your AB post, right-click where you want the link to appear and select 'Paste'
Job done!
I've just uploaded a random pic to remind myself of the technique. It's completely irrelevant to my answer but here it is anyway!
http://i42.tinypic.com/i5rm1l.jpg
Chris