Is repentance from indicating sin or from committing it a condition for the forgiveness of جاری sins, and does the sin of friends seeing a picture of an unveiled woman fall on me because of my comment, or on the one who posted the picture?

Indicating sin is in itself a sin, and its perpetrator must repent to Allah Almighty, for the one who points to evil is like the one who does it. There is no harm in commenting on a picture of an unveiled woman or a video clip containing something forbidden if there is an overriding benefit in doing so. Publishing it is not sinful if it is not intended to help others view it, and whoever comes across it must avoid what Allah has forbidden.