Just download the pictures to your computer and save them in a file. On here, click the "add new post" button so that you get the full screen to add a post. Click the paperclip button and a window will pop up. Browse for your file, then click upload. You can then close the window. Put your cursor wherever you want the picture to appear in your message, and click the little down arrow next to the paperclip button. Click on the tag that appears below (your image's number) and it will be inserted into the post. If your setup is different there is an alternate way that I can explain to you, but I think this is the easiest personally. Hope this helps.
From what you said it does sound like a very stubborn case of fin rot. I'll post more later.