Alternative controller for LEGO NXT
I would suggest Arduino or, preferably, Raspberry Pi.  Here's some info extracted from my previous answer on NXT: 

Arduino &amp; Raspberry Pi are flexible development platforms and they can easily be interfaced with other devices. As for image processing the Raspberry Pi would be the better choice since it is more powerful.

Arduino &amp; NXT:
There is a lot of Arduino-NXT hardware components that you can buy or even make yourself.  For example you could use this Arduino shield called NXShield-D and it's software.

RaspberryPi &amp; NXT:
Pi is a full computer and very easy to use.  To interface with NXT you can use the GPIO pins but thanks to the USB port, somebody already made the NXT-python to control the NXT brick.  Being a Linux system you'll probably find some ready-made image processing samples all over the web.