If my website allows uploading images (which are not moderated), what action do I take if a user uploads child pornography?

I already make it easy to report images, and have never had this problem before, but am wondering what the appropriate response is.

My initial thought is to:

• Immediately delete (not just make inaccessible) the image
• File a report with the National Center for Missing and Exploited Children with all information I have on the user (IP, URL, user-agent, etc.), identifying myself as the website operator and providing contact information
• Check any other images uploaded by that IP user and prevent them from uploading in the future (this is impossible, but I can at least block their account).

This seems like a good way to be responsible in reporting, but does this satisfy all of my legal and moral responsibilities? Would it be better not to delete the image and to just make it inaccessible, so that it can be sent to the National Center for Missing & Exploted Children, the police, FBI, etc?