1. A projection system comprising: an image projector to project video content; a processor to compare successive images of the video content to determine a non-changing portion, and to assign an object within the non-changing portion as a reference line; at least one sensor to detect position, motion, or orientation of the image projector; and an image orientation device configured to modify the video content in response to information provided by the at least one sensor to cause the reference line projected by the image projector to remain aligned in a predetermined orientation along a projection surface regardless of yaw, pitch, or roll corresponding to the image projector.