Nope, not gonna get into the post count thing. Beat to death.
But as far as images go, well, you can post them. Don't use the Post Reply box at the bottom of the screen - click the post reply button at the bottom-right of the last post on the screen. This takes you to a screen that looks like
this. Click the IMG button, and a window opens up where you may post the URL of the image.
If you don't have images stored on a public server, you can still attach the image as a file for others to download - there is a size limit, however. The Attach File box is near the bottom of the screen.
As a personal aside, I'd recommend you keep image sizes small. Some people are relying on dial-up connections to access the board, and large images really slow down page loading.
phpBB is cool - I've had one up for over a year - but this package has everything phpBB has and more.