The official Pidgin QQ support disappeared quite some time ago after it stopped working. However, there is a Chinese project on Google Code that is currently delivering a working Ubuntu deb package. On my Debian testing machine, to /etc/apt/sources.list, per  I added
deb http://ppa.launchpad.net/lainme/libqq/ubuntu precise main
apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 7C24E5AB949045F5
to avoid key complaints in the install, and then:
apt-get install libqq-pidgin
followed by a Pidgin restart, and QQ appears as an account option. All I needed to authenticate were my QQ userid and password, it just worked, and so far no sign of those annoying captchas!
Lord, am I glad to get rid of those official, closed-source QQ clients! Running that stuff, even WebQQ, on my personal machine gave me a SEVERE case of the creeps. Mind you, it must be noted that packages pulled from PPA are unofficial, but they are 100% Open Source with the code available for all to see, and I am seeing at least five people declared as working on the project. A worthy project for someone with free time....