Sure, ok....
First thing I do is make sure I have two tabs open...one for the forum, the other for my picture-hosting site (in this case Dropbox.com).
In my image-hosting site tab, I find the image I want to post and left-click it to be sure the the image loads in it's full resolution.
Then I right-click the image, and select "Copy Image Address".
I come back to the PRS Forum tab and click the "Insert Image" icon (looks like a little mountain range inside of a picture frame).
The icon box will pop up requesting an "http" address. I right click the address field and select "Paste". The address I just copied from the pic-hosting site should now be in the address field. Then I click "Insert".
Repeat the process for all the images you want to share in the post.
That should do the trick...