The only resemblance in most cases are the long twintails. Things like post #877328, post #645518, and post #485400 don't have the two girls looking alike at all.
I agree with jjj14 in that I don't think they should be tagged look-alike. It is not a resemblance that inspires the connection, but the song Black Rock Shooter. The current look-alike images of BRS are all related to Nakano Azusa, and that one makes sense because her hair color is at least rather similar and the resemblance is the sole reason for the connection.
