Thanks all people who helped me with this contribution/profile thing!
I think I'm now going to the right direction.

Thanks!! 

There are lots of possibilities, Bonus materials on discs will sometimes mention (uncredited), screen caps and/or time stamps to help in identifying the individual. An actor's website, which migh mention such work. The more documentation the better. Be wary of Online sources, unless you can line up several unrelated sources which is pretty hard to do, a lot of websites license their data from elsewhere. (Uncredited) data because of its nature is the perfect place to plant tracking data (poison pill) in ordere to be able to spot violations of their copyright.

Skip

Captions, especially Closed Captions, can sometimes be helpful, too.  I am in the midst of profiling the first season of Pickett Fences.  Like many US TV Series, role names are not given for the principal guest cast - so I've been starting to use IMDB (gasp!) as a jumping off point for those role names, then modifying them based on watching the episode itself.  In one episode, a credited actor played a doctor ("Surgeon" according to IMDB.)  While he was never identified by name on the soundtrack, the Captioning showed his character name along with his spoken line (e.g., Zawoski: [dialog]).  This may not be the best way to get credit information, but it IS on the DVD.