You need to have the picture hosted somewhere such as Photobucket first (Photobucket accounts are free), and then paste the IMG code for that picture into your post.
For instance, the IMG code for a pic of the Kaizer Chiefs' badge I stole from the net is
[IMG]http://i2.photobucket.com/albums/y40/Plynkes/Kaizer_Chiefs.gif[/IMG]
So I paste that in and the result is this:
There is a thingy you can click on in Photobucket that automatically copies the IMG code for you, so all you have to do is paste it here.
If your pics are already hosted somewhere, just post the pic's address with the IMG bracket thingies at the start and end of the address like they are in my example, or press the Img button on the forum control panel at the start of the address and again at the end.
And sorry for the hijack, I love the book in question, too. It was the second inspiration (after the book and film of "The African Queen") for the African Lakes project on my blog.