Hi Viktorie,
If I have a collection that someone else has determined I just put "Det. - Jane Smith," for example, on my label. I suppose that you could also add a note that the determination was confirmed by sight via correspondence with "John Doe" on the online taxonomy forum Ascofrance. I think that the level of expertise from taxonomists here on Ascofrance is high enough that in cases of very confident determinations it is ok to simply include the name of a particular investigator who gave you an opinion under "determiner". But yes, in the cases of poor photos and ambiguous determinations you could always note something like "Ascobolus cfr. furfuraceus" and then "fide Jane Smith," for example.  Perhaps even a note that the determination or opinion was made via correspondence with person X in the online taxonomy forum Ascofrance.  Best - Jason