From Liquipedia StarCraft Brood War Wiki
Ad banners are displayed once users log in to a server. Users are able to interact with these ad banners by clicking on them to open a link in their default web browser.
StarCraft only supports PCX and SMK ad banners. The PCX format allows for still images while the SMK format allows animated images, and both only allow a palette of up to 256 colors.
Ad banners are 468 x 60 pixels large.
To begin creating your SMK ad banner, you must download and install the Old Smacker Tools.
- Note: The latest versions of Smacker Tools(now integrated into RAD Video Tools) reportedly only displays for Mac clients. The Old Smacker Tools unfortunately only works on Windows XP
- Run smackerw.exe and then click on the Smack (compress) a graphics file.
- On the left side, navigate to the folder where your ad banner is stored and select it.
- Under Options, click on the Palette tab. Check Total palette colors to use:, set it to 64 and check Starting palette index to use:, set it to 32. Set 8-bit input palettes to Create new.
- Click on the Frame tab and check Create ring?
StarCraft should send packet 0x15 on login and every 20 seconds thereafter. The server will then reply to the packet with information necessary to download and display the ad banner. Whenever an ad banner is clicked, packet 0x16 is sent to notify the server.