Claiming a dependent for which he obviously wasn't entitled is probably a good indication of his moral fiber and why he was incarcerated to begin with.  You can still paper file your return claiming your daughter and then deal with the a letter from the IRS down the road asking who is really entitled to claim her.  For the record, the parent for which the kid stayed more than half the nights in a year wins.  If dear old dad spent 8 months in prison, I think it is going to be pretty tough for him to prove he had custody for more than half of the year.