We describe an automatic classroom capture system that detects and records significant (stable) points in lectures by sampling and analyzing a sequence of screen capture frames from a PC used for presentations, application demonstrations, etc. The system uses visual inspection techniques to scan the screen capture stream to identify points to store. Unlike systems that only detect and store slide presentation transitions, this system detects and stores significant frames in any style of lecture using any program. The system is transparent to the lecturer and requires no software or training. It has been tested extensively on lectures with multiple applications and pen-based annotations and has successfully identified "significant" frames (frames that represent stable events such as a new slide, bullet, figure, inked comment, drawing, code entry, application entry etc.). The system can analyze over 20000 frames and typically identifies and stores about 100 significant frames within minutes of the end of a lecture. A time stamp for each saved frame is recorded and will in the future be used to compile these frames into a jMANIC [16] multimedia record of the class.