Also once you've attached an image, you can use it in the future with the img tags.
Go to your User CP
At the bottom of the stuff on the left is "Attachments"
Click on that and it will open up all the images you've uploaded as attachments (it's a good idea to name the photo when you upload it so you know specifically which one you want to add in a later post).
Click on the image and it will open up in a new window.
Cut and past the URL to your new post using the img tags Like this:
[img]http://www.christianforums.com/attachments/76375d1150722930-scarbeer1.jpg[/img]
It's a photo of my cat licking condensation of a beer can that I posted 3 or 4 years ago and that would produce:
eta - blurgh, I thought I had resized that. Oh well, it's so cute I'm going to leave it up. And it was 5 years ago.