Interferometric particle imaging (IPI) is a robust and popular technique for measuring particle size and velocity. A method based on a template matching algorithm and an auto-correlation method is proposed to simultaneously extract the location and the separation of doublet images of a particle from an IPI focused image. The position coordinate (x,y) of the particle can be determined with high accuracy, as evaluated by using a serial particle mask. Furthermore, the method can be employed to achieve sub-pixel spacing extraction when combined with Gaussian interpolation. The algorithm is tested using synthetic and experimental data. The results suggest that the method presented here is promising for its application to a high-density particle field, in accurately measuring both the particle size and its location.