To add a picture to a post, first click on the yellow square icon in the editor. It's in the quick reply and the advanced editor, so it's always available. It looks like this:

Signatures can be added or changed as you like. Go to "Set Your Options" or click on "Quick Links" and you'll see the Signature link. You can preview it first if you want, change fonts or colors or add a link.

I hope this helps. If you have any other snags with the new boards, please don't hesitate to PM me, I'll answer as soon as possible.