ICQ has a feature to show your online status on a web page. You need to enable it in the "Security and Privacy" settings as indicated on ICQ's support page.
Once you include
http://status.icq.com/online.gif?icq=<ICQ-ID>&img=5 in a web page you can show your online status like this: (Online) and (Offline).
Now the page that used to show all the icons available (
img=<number> parameter in the URL) 404's (with a very nice 404-cow). Try at http://www.icq.com/features/web/indicator.html whether ICQ fixed their pages.
helped to get the Online (and similarly the Offline) icons in the mean time.
Looking at them I find these icons provide a nice glimpse into web design history.
ICQ was founded 1996 and has seen a lot of changes between being sold to AOL 1998 and on to mail.ru in 2010. Aah, the '90s ... animated gifs anyone?
As you probably risk eye-cancer looking at them too long, the full glory of the available ICQ icons delegated to the full article view...
So these are the icons for on- and offline status from ICQ retrieved 11.02.2012:
|Num||Online Icon||Offline Icon|
The empty (looking) offline icons have been intentionally created this way by ICQ. Probably because "who's online" pages with many accounts look less cluttered if only the online users have visible icons. How they managed to get Offline icons #18-20 to 811 Bytes while the Online ones are around 500 Bytes may remain their secret. The smallest empty (i.e. transparent) 1x1 GIF possible within the file format specification seems to be 43 Bytes. See Perlmonks - World's Smallest GIF.
20.07.2014: Looks like ICQ broke that web status feature. The status.icq.com URLs still redirect to online and offline images but these are not served from their web servers anymore, so calling http://status.icq.com/online.gif?icq=197344872&img=2 will get you redirected to http://status.icq.com/27/online2.gif but that is giving a 404. So ... time to leave ICQ for good.