I've had similar problems and found the case identity by doing a Google Images search against the movement number. It's simplified if the case has a square/rectangular crystal as on those the case numbers start with '5' so a search of say 'Seiko 6119-5000' or 'Seiko square' throws up lots of similar cased Seiko's.
Similarly divers case numbers start with a '7'. Google is your friend
Thanks John_D, had not thought of that though I didn't know about the start numbers of the various cases, I'm new to this and don't know very much about the names and numbers yet, sometimes it seems everyone else is speaking a different language
The Japanese Watch Photo Database that can be accessed from the forums page of this website can be helpful to identify watches. It pays to double check if only 1 watch is listed as I know at least one is incorrect.