Distributed acoustic sensing (DAS) transforms submarine telecommunication cables into densely sampled seismic receivers. To demonstrate DAS applications for seismic imaging, we have used an optical cable on the seafloor in the Trondheimsfjord, Norway, to record seismic data generated by a controlled seismic source. The data are simultaneously recorded by a towed hydrophone array and the fiber-optic cable. Following our data processing methods, we can produce seismic images of the seafloor and underlying geologic structures from the hydrophone array and DAS data. We find that the hydrophone and DAS data have a comparable signal-to-noise ratio. Moreover, DAS images can be improved by using a seismic source that has sufficiently large energy within the frequency range matching the spatial resolution of DAS. The temporal resolution of the DAS images can be improved by minimizing the crossline offset between seismic sources and the DAS cable. The seismic images from DAS can be used to support geohazard analysis and various subsurface exploration activities.