From Sonic Retro
Sprite comics are web comics that use video game sprites and backgrounds for their artwork. Sprites are pixelated renditions of video game characters that are taken from ROMs, through computer emulators. There are also animated sprite comics, where each "strip" is a separate mini-movie, some utilizing Flash for enhanced effects.
Bob and George is often mistakenly recognized as the first "true" sprite comic. Originally planned to be a regular online comic, the creator started off with Megaman sprites as filler. When he finally got around to the real comics, he found the Mega Man sprite comics were more popular, and he reverted to them. Despite this, however, the first sprite comic strip did come from Bob and George.
Some of the better known sprites used are from games like Final Fantasy, Sonic, Metroid and Megaman. The main reason for this is the wide variety of poses the sprites from these games have, and the ease with which they can be edited into new sprites.
There are, however, many sprite comics that use a combination of several spriting techniques and styles. Comics like How to Make a Sprite Comic in Eight Easy Bits use a combination of original and ripped sprites, while comics like Shagy Comics use ripped sprites from several different games.
One form of webcomic similar to sprite comics are pixel art comics. The major difference is that in pixel art comics, the sprites used are wholly or mostly created for the comic, rather than being pulled from video games. Two good examples are A Modest Destiny and Kid Radd. Some hand drawn comics, such as Tsunami Channel, have been known to have spin-off comics created using original sprite versions of their characters.