Oh, it's Napolean Dynamite.
Karmic: when you see a picture on the web, left click on it. At the bottom of the menu that pops up you'll see "properties." Click on that. In the middle of the window that pops up, you'll see the url for the pic. Copy the entire url. (The thing that starts "http://...")
Then, in your greasespot post a reply window, click on the square between the envelope and the >. Paste in the url from the picture you've found. Hit "Ok."
Do that for each picture.