To post a photo in your message OR the sig line, ditch the links and HTML and just copy and paste the picture itself. Either right click and copy - or Highlight the image and hit CTRL and the "C" key (to copy). Then click in the box you want to place the image. Click ON the flashing curson in the box. Then either right click and choose paste OR hit the CTRL and "V" key on your keyboard to paste the image.
To resize the image (BIG images really slow load time!) - click on the image in the box. That puts little resize buttons on each corner. Grab one and drag your image smaller.
To single space: Hold down your shift key while hitting enter. This allows for one line down instead of the double space. Makes for a neater sig line - IF you like. :o)
Hope this helps!