The image displays just an image. The camera display will display the image with renderings of other data in the scene rendered on top of it, but in order to do that it requires /tf data that creates a tree between the "fixed frame" (set from the "global options" group in the "Displays" panel) and the frame that the image is in (this is determined by the value of the "header->frame_id" that is published within each image message).
So probably you don't have /tf data to show the image in the camera display. You can work around this by setting the fixed frame to be the same thing as the image's frame id.