AFAIK "/getimage" is deprecated in CDH and we suggest this not to be used. Instead you can use the command "hdfs dfsadmin -fetchImage <dir>" to download & save the latest fsimage.
Based on research, in earlier versions of CDH, the getImage method was available after which a need was realized to provide a proper command/utility to download the FSimage and as a result of which "hdfs dfsadmin -fetchImage" was born. Once that was put in place, the getImage was removed.
Does that answers your questions ? If yes, feel free to mark this post as "accept as solution"