Background light affects an image and degrades its quality. Laser lock-in imaging is an outstanding technology for reducing the impacts of the background light by a sine auxiliary modulation. However, the technology is expensive and not safe enough, and it requires that the frame rate of the image sensor is high enough to meet the modulation speed. In this study, the technology is extended theoretically to investigate the feasibility of a non-sine auxiliary-modulated light and mechanism of the background light elimination. We used an LED as the auxiliary light and the control mode of optimizing image acquisition to reduce the requirement for the frame rate of the image sensor. According to our findings, the modulation signal of the auxiliary light of the locked imaging technology can be extended to any waveform signal with zero integration in a period. Experiments using sine, square, triangular, and sawtooth signals to modulate an LED light show that in a modulation cycle the proposed technology uses four modulation waveforms to achieve a good background light elimination effect at different sampling rates. The proposed technology has low requirements for auxiliary light sources and frame rates of image sensors, providing theoretical feasibility.