Their nude picture is good piece of evidence. It is relevant under section 62 of evidence act. it constitutes the ground for filing FIR for the offence of adultery which is punishable under section 497 ipc, if their pictures are taken after your marriage. You also get divorce on this ground, adultery is valid ground for divorce under section 13 of Hindu marriage act(HMA).
If it is taken before your marriage then no offence of adultery is made out but you can file divorce on the ground of her immoral character. If your marriage is not lasting more than one year then you can file petition under section 12 HMA for annulment of marriage because good character is essential criteria for marriage.