In this paper, we present a PDA-based face recognition system as well as some of the associated challenges of developing a PDA-based face recognition system. We describe a prototype system built from an off the shelf PDA, and introduce algorithms for image preprocessing to enhance the quality of the image by sharpening focus, and normalizing both lighting condition and head rotation. We use a unified LDA/PCA algorithm for face recognition. The algorithm maximizes the LDA criterion directly without a separate PCA step, which eliminates the possibility of losing discriminative information due to a separate PCA step. We demonstrate effectiveness of these algorithms and the feasibility of this system by experimental results. This system has many applications including information retrieval and law enforcement.