In 2010 Bifferboard was the smallest size Debian board. It's hardware was the same as for a NAS server. But it was NOT possible to re-program NAS server to make a Bifferboard. Needed to order from company.
Processor speed was only 150 MHz. RAM 32MB, small too. Power consumption from wallplug with a webcam, hub and USB stick was 4.5 W.
You can set up a HD webcam using mjpg-streamer using Logitech C510 or C270. Some example pictures are here:
Motion detector attached to GPIO with an endless loop in a sh script was not reliable. Looks like there was not enough RAM or there was a Debian bug: when many sh scripts run simultaneously they dissapeared from "ps -ef" list. Sometimes it happened after just 10s and sometimes after 7 minutes. Swap file did not help. Might be RAM defect.
Wi-Fi stick worked, but only for some minutes. Same issue.
If size is not an issue then in future projects requiring low power consumption would recommend to use OpenWRT router Wr703N.
Be prepared that Linux programming is not easy. Sometimes you need to Google for hours for a single line of code.
Below are my programming notes that could hopefully help you to set up Bifferboard faster. Sorry that they are somewhat messy. Hope thee notes can be useful to you when programming other Linux boards.