you should be able to post the picture by putting the direct link in-between the two image tags like this
[/img] image url here [img]
(just remove the / from the first img box, I had to put that there so the code would show up.
or
when making a post there is an option to choose to attach a file.
Try both of those and let me know if you have any issues. There might be some sort of limit of file or image size that I am unaware of, so maybe try with a smaller picture and see if that works first