In the field of laser speckle measurement, background interference has always been a major factor affecting the accuracy of measurements. Traditional Fourier component methods, while capable of eliminating background noise, are complex and prone to errors. This study explores the application of a speckle differential measurement method in laser projection images through experiments with one-dimensional and two-dimensional sinusoidal signals, as well as step signals, combined with data simulation and verification. The results demonstrate that this method effectively mitigates the interference caused by screen structure, brightness inhomogeneity, and pixel structure on measurement outcomes. Furthermore, it significantly enhances the accuracy of speckle contrast measurement. This research provides a simple and reliable new approach for the accurate measurement of speckle contrast.