Receiver accepts/denies pictures/messages
Make it so that the recipient has to agree to receive a picture from someone else in chat/messages/mail. This will prevent unsolicited offensive images from being seen.
Have an "Accept or Deny" message request from people that users AREN'T following. So they only accept messages from people who they want to talk to/follow.
Implement either a community monitoring system, or appoint mods from the community. The response time on abusive members who blatantly break the rules is unacceptable currently.
Secondly, how about restrict people from sending pictures via private message - either entirely, or without permission. Women being sexually harassed on your website is something you should take much more seriously. Tolerating a system where each offender gets to vitcimize several women a piece before action is taken is unacceptable - a reaction of 'just block them' is also unacceptable, as it allows the perpetrator to continue on harassing other women, and doesn't actually stop women from being harassed in the first place.
I'm pretty disappointed so far. I believe in hands-off moderatorship, but I also believe in addressing serious issues with a sense of urgency, which has been desperately lacking.