Automatic CAPTCHA By Matching Images?

I'm playing a simple textbased game. And then I thought why not try to create a bot. But there's one problem. A CAPTCHA...But this captcha is very simple. It's 3 random numbers wich always uses the same font, size etc.For the simplicity we can say that it uses 9 different images and randomly puts together 3 of em.I then remembered a client for a java game that matched images with text on the screen to read the text.How can I make a program that does something like this:

if imageA.bmp exists on screen then
captcha &= a
End If