Sorry, dude, wrong board.
You can put them in your sig by getting the URL of the image and wrapping it in img tags. Basically like this: [ img]theimageyouwant.net[/img ] but without the spaces.
Also, remember there are limitations on the type of pictures you can use. Check out the FAQs and rules and regulations of the site to find them out, or PM one of our staff (Richard, Goom, Pheonix, Estrid, Terenia (Am I missing a staff member? Seems like I am....)) and ask them.
This would go more in the suggestions and feedback board, FYI. But no worries, everyone makes a thread-placement booboo every now and again.