I use Imgur.com , It's a picture hosting site that will give you a link you can copy, that you can just post into the box that comes up when you click on the picture icon when you are posting a reply or new topic. After I post a picture to my imgur account, I open that picture and it will give me a choice of links. I use the direct link box and at the bottom it lets you chose small, medium or large.

After I click the picture (of a tree) icon in the rpod forum reply (or new topic) page. 

I delete the HTTP in the post link box

and paste the link I copied from imgur, (it has its own HTTP)

I then click the preview box to make sure it worked, and then the ok button at the bottom.

I usually use medium or large depending on what I want.

I know some here don't like imgur because of their terms of use, they are a social networking site and constantly try to get you to have your just posted picture go public. I keep all pictures private and only upload pictures that are not personal (90% forum goofy mods and such) So I don't really care who sees them. But on occasion a few have gone public and really confused the imgur army because I don't name them or describe them, and it's some close up of a piece of wood or something.

rgds John