You can't paste pictures from any browser. In your original post, there's an upload button you can use to upload the image to the first message post in the discussion thread. In subsequent posts to the same discussion, you can only upload the image to a file sharing site and then post a link to it in your post. With the right settings, your image will appear even when you upload it to a file sharing site.
You can also click the edit post link to your original post to upload an image to it after the fact.
What are the best file sharing sites...?
if you know a few that would be great my network is pretty tight because of our IT team so not all work.
Sharing sites are notorious for bombarding you with ad links and pop ups--some of which may deliberately be designed to look like the down load link or button just to get you to click them. These links may also contain objectionable images you wouldn't want your boss or a family member to see. Thus, I'm not suprised that Corporate IT would block many such sites.
Can't really recommend any to you. I use http://www.4shared.com/ but it's only a little better than some and worse than others.