Besides Raspberry Pi, many other low-cost SBCs are suitable for running a desktop Linux distribution and OpenCV applications. While the Pi uses a single-core ARMv6 CPU, some of the alternatives use dual-core or even quad-core ARMv7 CPUs that consume more power but can run more advanced computer vision applications in real time. Here are some examples:
Odroid U3: A $65 quad-core SBC. One of the Linux distributions it can run is Lubuntu, a variant of Ubuntu. Its official website is http://www.hardkernel.com/main/products/prdt_info.php?g_code=G138745696275.
Marsboard A20: A dual-core SBC that costs around $75 (or less if ordered directly from the factory). It has many connectors. It can run Lubuntu, among other Linux distributions. Its official page is http://www.marsboard.com/new_marsboard_a20_feature.html.
Banana Pi: A dual-core SBC that costs around $60 (or less if ordered directly from the factory). It is compatible with many Raspberry Pi accessories and can run numerous Linux distributions, including Lubuntu, Raspbian, and its own optimized distribution called Bananian (based on Debian Wheezy). Its official page is http://www.bananapi.org/p/product.html.
Of these alternatives, I have tested Odroid U3 (running Lubuntu) and found it capable of using OpenCV for face detection and recognition in GUI applications in real time.
If you would like to share your experience with using SBCs in computer vision projects, please write to me at <[email protected]>. I will post the community's wisdom to http://nummist.com/opencv.