I think the http// is to link to a picture you might have on a website like photobucket.com (or another site). Someone correct me if I'm wrong, as I do not download my pics that way.
The way I do it......
If you have your pics that you want to post stored in your computer, hit "browse" and then go thru the steps to get to your pics. For instance, I put my pics in a folder in the documents area. So I would click "browse" then choose "documents" and then choose the folder where my pics are and the choose the pic I wanted. And then I would repeat that until I have all the pics chosen that I want in the listing and then download them.
I hope that helps!