In-line holography systems have been designed and investigated using Novosibirsk free electron laser as a source of monochromatic tunable terahertz (THz) radiation. A thermograph, a thermal sensitive phosphor plate, and a microbolometer array were applied to recording of holograms in the spectral ranges of 128-160 m and 68 m, including recording in real time. Specific features of these devices are described in detail. Five methods of image reconstruction are analyzed and verified using recorded holograms. Prospects for the use of THz holography are discussed in brief.