That is funny to me as I do not know how to post thumbnail pics! I put my photos on my computer then transfer the photos I like to a "hosting" site. I use Photobucket and make them all 800x600 using the transfer tool. Then left click on the last url on the picture and select "copy" and right click in the S&W reply box and select "paste".

The picture will transfer. Select "preview post" to see the post and the picture will be there.

Kind of a confusing explanation but pretty easy to do after you do it a few times.