The bulletin board software doesn't have a specific button for "uploading into ROS", as you put it. What the bulletin board software does is it looks for a certain code tag with an URL from your third-party image site, and then the board software will show an image or link from that third party site based on whatever code tag that you used. If your site gave you something called BBCode, that's what you want. I've included an attached screen capture from my Imgur account to show you what it'd look like.
To show an image in a post from Imgur, I'd copy the BBCode text from the bottom right side and paste it in a post. If you have the image up in a browser window, copy the whole URL from the address bar, paste it in your post, put an [img]tag before the URL and a [/img] tag at the end of the URL.
It should look something like this, but I substituted !'s for i's so the software wouldn't try to interpret it:
[!mg]http://i.imgur.com/TbnRuZ7.jpg[/!mg]
If you have video uploaded somewhere like a Google Drive account or Dropbox, you can just add links in your post to the specific files after editing.
I hope that helped a little..