I can answer a little of this.
Yes, there are units in numerous agencies that specialize on these types of crimes.
When our office does the forensic exams, with the equipment we have, it can break many of the images into "known" CP and unknown CP. "Known" means these are images that have already been identified by NCMEC and victim info is often known. Unknown CP means just that, not already identified and further investigation is going to be needed to see if victim info can be determined.
NCMEC is our clearing house for CP. We send our images to them and it can take a few months for them to return info to us.
As I mentioned much earlier on in this thread, we had a local LE partner that our agency trained, that had to ask to be released from his 3-year commitment to us because of nightmares, anxiety, etc...basically, his mental health. Realize, he was a known officer to us before and hand-picked because he IS a great investigator. It just shows it DOES take a special person to be able to focus hour after hour on this type of crime and not have it impact your daily emotions.
A little off track of Jared, but I read a report on one of our exam returns just last week, and it was one of the most disgusting ones I have ever had to read. 5 victims in the images, and we now know 2 were ones the suspect manufactured - meaning, he (or, "allegedly" someone in his house, LOL) videotaped the criminal acts. Ages estimated were 2 years old, and 11 months.
(The others were ages of 7, 5 and 5, IIRC. Bound, items forced in cavities, etc. When you read articles in the media about CP, you don't normally get the "real picture" of how horrifying those incidents can be.)
Shower time.