Light waves transmitting in a multimode optical fiber (MMF) for endoscopic imaging, due to modal dispersion, inevitably suffer two severe distortions: on the way in for illuminating and on the way out for imaging, which becomes a big challenge when using a single MMF for endoscopic applications. In this paper, based on obtaining the optical transmission matrix of the MMF working in the endoscopic mode, we propose a new method for retrieving endoscopic images from speckle fields, where the two distortions could be eliminated simultaneously. Our experimental results demonstrate that the object images can be well reconstructed directly from distorted waves. In addition, no scanning operation is required when collecting images, which is timesaving. Such an efficient method might have potential applications for wide-field and ultrathin fiber endoscopic imaging.