The photoinjectors are promising high quality electron sources for X-ray free electron laser (XFEL). The uniformity of the electron emission from the photocathode has big influence on the electron beam quality. Usually, the quantum efficiency (QE) mapping is used to evaluate the uniformity in experiments. The QE mapping imaging method used to measure the QE mapping has high resolution and it can be used in real-time measurement, so far it is only used in separated type photoinjectors. In our photoinjector, the electric field and magnetic field are overlapping in the cathode vicinity, according to theoretical analysis and simulations, we analyze the application of this method in overlapping field. Finally, we demonstrate that the imaging method is suitable for this overlapping field, and the results show that the QE mapping has higher resolution in the center of the photocathode than the outer part. We also analyze the imaging method used to measure the transverse momentum distribution, and one way is proposed to judge whether the rest magnetic field on the cathode is zero or not.