I'll try to help on this one, as I'm a bit of a "techie" but sometimes it's hard to explain.
What I do, once the image is posted, is I RIGHT click on the image (using a mac, hopefully it's similar on a PC) and "Open the image in a new window"
Once you have done that, you should have a web page open with JUST that picture on the page.
Copy that URL and paste it between the (img] (url) [img]
See if that works.
If it doesn't, keep asking. Once you figure it out, it's easy. Until you figure it out, it seems impossible!