There are two issues tax and legal problems. the IRS only recognizes custody. so if you have custody you can claim the child unless you provide the father with form 8332. however, violating a court order will get you in legal trouble with the court if the father pursues the issue. you should get legal advice.
if you both file claiming the child, the IRS will send each of you a notice asking each to amend. if neither does then the IRS will send a second notice asking for proof. the one providing the best proof gets to claim the child. however, as stated if this is in violation of the court order then there can be legal problems
