Container cranes are traditionally operated by operators who work inside the crane's cabin. Nowadays, there are also container cranes that can be operated remotely from control rooms. The change from on-site operation to remote operation introduced a new problem called the lack of depth perception. Operators of remote container cranes rely on the video stream shown on their monitors to see the remote environment, but it is more difficult to estimate the distance between existing objects based on the view on flat screens. The lack of depth perception could increase the risk of collisions since it reduces operators' capability to lift and stack containers accurately. This paper proposes three types of graphical user interfaces (GUIs) that could improve depth perception in remote crane operation. The first GUI visualizes the shadow of the crane's spreader or the container, while the second GUI shows four perspective lines from each edge of the crane's spreader or the container. The third GUI provides the x-ray vision, which highlights the edges of the container and makes the container semi-transparent. We involved seven remote crane operators in an experiment, where they had to move ten containers while using either of the proposed GUIs and without using any additional support. The results suggest that the shadow interface and the line interface provided better outcomes than the condition without having any additional support in terms of completion time, stacking accuracy, number of collisions, as well as perceived workload and usability.