I referenced http://en.wikipedia.org/wiki/Image:Calamity_Jane_on_a_horse.gif
no go (that's Calamity Jane)
I referenced
http://www.outlawwomen.com/PokerAlice.jpg
for Poker Alice - no go
The only thing I can think of is that these addresses won't allow referencing. I'll try again.
They do, you're just not entering the HTML correctly. Type it into your message like this:
<img src="http://www.outlawwomen.com/PokerAlice.jpg">It'll come out like this: